public class FibonacciGenerator
{
//instance variables
private int recent ; //one values ago
private int previous ; //two values ago
private int n ; // the number of values returned so far
/**
Constructs the generator by setting the instance variables to 1
*/
public FibonacciGenerator()
{
recent = 1 ;
previous = 1 ;
n = 0 ;
}
/**
Produces the next Fibonacci number
#return the next in the Fibonacci sequence
*/
public int next()
{
n ++ ;
if (n == 1) return 1 ;
if (n == 2) return 1 ;
int result = recent + previous ;
//----------------Start below here. To do: approximate lines of code = 3
// 1. Update previous and recent, and 2. return result.
previous++;
recent++;
return result;
//----------------------End here. Please do not remove this comment. Reminder: no changes outside the todo regions.
}
}
import java.util.* ;
public class FibonacciGeneratorTester
{
public static void main(String[] args)
{
System.out.println("The 1st Fibonacci number is: "
+ getFibonacci(1)) ;
System.out.println("The 10th Fibonacci number is: "
+ getFibonacci(10)) ;
}
/**
A static method to return the n'th Fibonacci number
#param n the index of the Fibonacci number
#return the n'th Fibonacci number
*/
public static int getFibonacci(int n)
{
FibonacciGenerator generator = new FibonacciGenerator() ;
int result = 0 ;
//----------------Start below here. To do: approximate lines of code = 4
// 1. Write a for-loop that calls the generator n times 2 . return the last result of the call.
for (int i = 1; i <= n; i++){
generator.next();
return result;
}
}
}
missing return statement second last curly brace highlighted. Is my for loop correct?.......................................................................................................................................................
Your for loop begins:
for (int i = 1; i <= n; i++){
If n was less than 1, it would immediately exit, and there is no return statement between the end of the loop and the end of the method. That is the missing return statement.
Look at this:
public static int getFibonacci(int n)
{
FibonacciGenerator generator = new FibonacciGenerator() ;
int result = 0 ;
//----------------Start below here. To do: approximate lines of code = 4
// 1. Write a for-loop that calls the generator n times 2 . return the last result of the call.
for (int i = 1; i <= n; i++){
generator.next();
return result;
}
}
It must return an int. Look closer at your loop. What is n = 0?
That's right it won't return anything. That is not allowed here.
public static int getFibonacci(int n)
{
FibonacciGenerator generator = new FibonacciGenerator() ;
int result = 0 ;
//----------------Start below here. To do: approximate lines of code = 4
// 1. Write a for-loop that calls the generator n times 2 . return the last result of the call.
for (int i = 1; i <= n; i++){
generator.next();
}
return result;
//put a return statement here, instead of in your loop.
}
TRY THIS CODE:
import java.util.*;
public class Fibonnacci{
public static void main(String args[]){
int num;
Scanner in=new Scanner(System.in);
System.out.println("Enter an integer");
num = in.nextInt();
System.out.println("Fibonacci Series");
int sum=0,a=0,b=1;
for(int i=0;i<num;i++){
System.out.print(" "+sum);
a = b;
b = sum;
sum = a + b;
}
}
}
Related
Ok so I been working on this assignment all day for the past 3 days but I haven't had any luck. I wasn't going to ask for help but I finally gave up. But there is also one more thing I need to implement to the code. This is what I gotta implement "Find the length of the longest continuous series of positive numbers in the array data. If the contents were: 4 5 0 2 . . . -1 88 78 66 -6. The length would be 3. For this problem, 0 is considered non-negative but not positive". Plus I have an issue where I can't print the largest int in the array of 20.
import java.util.Random;
import java.util.ArrayList;
public class arrayops {
public static int findLargest(ArrayList<Integer> nums) {
int greatestnum = nums.get(0);
for (Integer item : nums) {
if (item > greatestnum) {
greatestnum = item;
}
}
return greatestnum;
}
public static int randomData(ArrayList<Integer> nums) {
int[] array = new int [20];
Random random = new Random();
for (int i = 0; i < array.length; i++) {
array[i] = -100 + random.nextInt(201);
}
return -100 + random.nextInt(201);
}
public static void main(String[] args) {
ArrayList<Integer> nums = new ArrayList<Integer>();
nums.add(1);
nums.add(4);
nums.add(13);
nums.add(43);
nums.add(-25);
nums.add(17);
nums.add(22);
nums.add(-37);
nums.add(29);
System.out.println("The Greatest Number from the hardcoded numbers " + findLargest(nums));
System.out.println("The Greatest number from the random numbers " + randomData(nums));
}
}
The findLargest method:
public static int findLargest(ArrayList<Integer> nums) {
int greatestnum = 0;
int greatestLen = 0;
for (Integer item : nums) {
if (item > 0) {
greatestLen++ ;
if(greatestLen > greatestnum)
greatestnum = greatestLen;
}
else
greatestLen = 0;
}
return greatestnum;
}
Logic used:
Keep the length of the longest chain encountered, and the length of current chain, in two separate variables (greatestnum and greatestLen respectively)
Increment greatestLen every time a positive number is encountered. If the number if less than or equal to zero, reset this count.
If the length of current chain is greater than the previous longest chain, sent the longest chain size to current chain size.
The problem is you created a list with random numbers but never put that list into the findLargest method. You also never created a method to find the consecutive positive numbers. If you didn't know how to go about coding it, I recommend drawing out an algorithm on paper.
Largest value in ArrayList...
public static int findL(ArrayList<Integer> nums)
{
int top = nums.get(0);
for(int i = 0; i<nums.size(); i++)
{
if(nums.get(i)>top)
{
top = nums.get(i);
}
}
return top;
}
Largest number of consecutive positives...
public static int positiveString(ArrayList<Integer> nums)
{
int longest = 0;
int count = 0;
for(int i = 0; i<nums.size(); i++)
{
if(nums.get(i) > 0)
{
count++;
}
else
{
if(longest<count)
{
longest = count;
}
count = 0;
}
}
return longest;
}
If you want to arrange the numbers into order you can simply use java.util.TreeSet. Then use the method last() to get the largest number.
public static int findLargest(ArrayList<Integer> nums) {
return new TreeSet<Integer>(nums).last();
}
static int count = 0;
static long[] cache = new long[3000];
static {
cache[0] = 1;
}
public static void main(String args[]) {
for (int i = 0; i < 100; i++){
factorial_with_cache(2999);
}
System.out.println(count);
}
public static long factorial_with_cache (int n){
if (cache[n] != 0){
return cache[n];
}
cache[n] = n * factorial_with_cache(n - 1);
count++;
return cache[n];
}
I built a function that calculates factorials using a cache (ignoring overflow).
But its runtime isn't any better compares to non-caching function and I found that caching isn't working correctly.
Because I expected a variable 'count' to be 2999 after loop but I fount it is 293465 which is a lot more than that. (without loop, it prints 2999)
What is to wrong with this function?
It is because the range of long datatype:
long 8 bytes (-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807)
your factorial gives the positive values till you are searching for factorial of 25.
And latter 25 , the value of factorial which are calculated is coming negative (It means you are overflowing long) and your count will work as expected till 65 factorial is calculated (till negative value) and then the value for factorial 66 it reaches to 0..
just try below by printing factorial:
for (int i = 0; i < 100; i++) {
long fact=factorial_with_cache(66);
System.out.println(fact);
}
System.out.println(count);
And the count will be printed as
(forLoopCount*(number-65))+65 , In your case (100*(2999-65))+65 is 293465
becuase the value for factorial it traces back in cache which is not zero is 65th element (at 64 index).
So, let me break it down to you!.
The factorial value of 2999 is 13831198678126180285189556976955373903170397316439366392298225525658528550411773166953335884059334473358394878461205706165250290371348635931517800720356113203873679301399725840687554463393227601721573232498656280819242922032367667908703698446747042372944385912938442812976579204340368770976791467161792908482026536763476497016597962706920837208377639001547222987372530067858391829660217859289638428364594156664891566396944031170356121274762354507422848113071258383496196034678939603033097637499047300169646331468238450491051510529147169986724755958362486789324705690789582425714662973561230539501202732819906031261484507986168459203695503720787715306962036185816958171315101812071237299383615730698142124734425009998777928314671591890471560274735833304904959453223240212984890196653392856493421129589037623689334983609133572374939825462133789731181451373437595533811597516653047843373551034468875167743673579450500731701049557870779579798365517154053116338596649981357437001475641612713380485162624246015285341187194401439315317685276897783748963573748717156161769574677089322363037849660911158458585633121725465474927244487503626338581145799640164089032772344644035725447994450814858680158855133471471566493328118184865933128900946476171137729637721898436949504508364668715924682335777135513931476001478897301228489756952423900549337170685817482869322924594934553551003036605213030431370211238540513634600045019557208087444634144722209572173742863424856277834965975623123264292792298280478857955478985025157988294085407394460004866920398953072534411602822485072110137246001443714741975414563519594304969324628586261528579942898463434127945755294142551435479172585965738348357120600576683876141492098075828585209276254499589065093789637861306274833094913863894376778010733315584027638295254781954610771181735025318637354022424432317128707664886202509105961484149955116054723079614963020498616978124480963271628142440605710424177963844835527047941127068625126602868360296587251294298750977877916818183056200089076530408509618194827562218441437670451251604136520412562026002566902646513949635716489125951469176102624329367970981707309954931234483752478815193819919046940901995441721784302194857041195090070644484327035189466269961364993448728359341757679578928014056475745993488101416681676935545677586672113973814268569600810283522630702882325818379846373279545389063433426048793378977494110923865060198731023168079278694206856962403099309932476468192292446106625814895181431600107247018896474570181676290139870638357579666677214004824737774431290539343185204668200955800140961796618216776009476171707432009598580600540607745366106990480349004177689104965384412262911661517983201465683450782588737131971506423474040743808999564029154506993562074784937792064798377314289371162177187409391071658827235127282051775532062510098826200386957421213481307419200642164870305628383671047981858132767730852384720717147489707456839716365953949812050321036644546531520598864465617319535112877058774715688947419064131580843908826519916664427749093269298823584351338064696733536570891584395455175134404252585951310232510018865069402485833157299381484590749402629481111706181867189617902727630965072766713218125649095472925555254271796579113386470181227145145782044748230689023360927474548519150294185556719080917603439047213543803560461443641342427106320294937680221742056517608545727954154981431896286464615575574564733158523773515339421141910343038451177576269394257673865595696145764470705694837193543322565755533887878425653323007167374034984753189092864395172089482366791478206807334511797067912797698473565007162069130217730303607114778083832632094745399523891591282708699147685012083622118240243657099361565732179240926631053400186908352669170802498149387797404799372830916093992885059492849249732904712828347430127984696856947346045759045222567855013693926840231677378744507230913510338446973920611359605911891548916357205533551076812967546595355169668436624145148563105200443314135704098338484590507017314148504265121657071624074064576429719944333914132659197510167106279294498294744074169106272133146311875939034291810862931519619247593463572388793752634599383049481842295290543310338170244405184924421525345305394766236107745856279305711691002008912764098229027010250648673458812712892369111259770860752452145178192387601343493641928636582411137977634690746620001816089765370131213375846513299799140007308422976207521653093045456515661082438164698099164737736238987887604321282063792704869736900344337373311421647222149710103632831178455467277094227704168859462141968845732336969092143110178250432445572309805015956983080592707178326499816577452815043403343240119997858835910187898983513330297084001603373363523211048122726398082654521129700828750257789083133267241150542349616716479447911942146684493824985807109624549493196517947945459425200477792599605375618154135498044805373036317551108920542553407043626403888641459832178279343412021431660661847004770522200579839513142002891066188195561545147576726674097535863255730732789176509455052905173962566105999668617707172897012592225627884763749139942033144845223843137607945870705185228736818194603451718134984572823575454406177591828833937000873777076143286975370719857688674644025825580933636487558107379601763547689237092321337911968750350350207856080439217177676925119658378188382474722467172490240279700623329997759788303630895974913235271384285181321984740867973019755275212448225468786508612988993837327986628867894584347339330109395315189804183506355434284956511125894328200010602697940710012700738129019153727101417320638801990152011727707236050552882452185513510976137249542985694285597433351175282125687093530484011848796644042625302116542612658623784196206071084087859012798734245795108302784560165996695233840827767813175065781551114331550855078698914278183507913244634124753936290599761240761788764479746965254304384814035524536401827280713121964622571847614159091700055578119247697879649481521588125728024624793157002622383690149851552542093855379183576921256026866677281432077992602744437119929192378994337605857208557227762427170645778895263145703032582860407622708941374105757560394991735954484369165110569420051053146751215121841484529317344915071143082972214834934785117427325907327323956351628058965466260901594022042307157516206082619875478093063424834484331589789332405761721821863933157263022628562426191490028096574592744921026913639837655412782142613217955005774888616730714697231543457088527065900258227520678399439594304530337999272434545057921568904794664270097074820282773506327749449618377008513240527728310551223577424390998477250258491878249375773652218477283959862326057497240566955256032969442610279413479245991485114175229570966285171060322337499286484763536542456863553323594724246140240535192263020188389231521830040129388591953979743641454327796516619093291507799363499952822494950133169703132944736808231037872625326203934365369591454254996804885055848502537888575304997792038113414587636763461378629510437530377514949741965335728283723130064661811549805161260779434177122925330001814574110967154189394698666276840840528442866611330112198472977565560054421966452744887749026774673476597119141918499516457632064030550264890665707146610860517981945041882670296628962352294237074209578011924139474934410391009112814073534671869747359856497734981269800821854176767776274721767346002013762814794961396376464661990588556737167203780040389785178621661600980521079426482525438347561911423287705520933644054859388470137299692798736919535048363842176140811215743626823029475470841708861576378019731723918097050874000743252328975986374873654787685684044366405474086145883963064543443283741094316935375400191188518071061185279429772712931980320767930925743448141144113853867852863500774825091500876956610471375132123918137870632423052883572240769361145098526133695745342449000372928715411061813143685686161256824935345001518961673534243407418799210246313328341659385060893305664721381846776636604396835551452718885897176356302728734712814697152118430414021633905812143491151730458640971651094329383936246692244495665898440957150263861482901326801912557851925957864645963859049318674446902818797438056706130851744872706591971891128651973088423541354578092586738615503678456019321106904965647554452856791768609892202741402821821519518889296407542539996754653930879152617217513639585536181286553740648082906808320000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 find it yourself
I know its a lot of scrolling :P
Okay, now during your iterations, factorial of 20 will be 2,432,902,008,176,640,000 and factorial of 21 will be 51,090,942,171,709,440,000 and maximum value for long in java is 9,223,372,036,854,775,807 so, here your cache[19] will be -4,249,290,049,419,214,848 and cache[65] will be 0. which makes all values till cache[2999] to 0. So, every time you call the method factorial_with_cache, it's not serving from cache, but calculating every time (because you're checking if(cache[n] != 0) then return from cache else calculate) causing the count value 293465 instead of 2999.
I've modified the code a little for your understanding.
public class Test2 {
static int count = 0;
static long[] cache = new long[3000];
static {
cache[0] = 1;
}
public static void main(String args[]) {
factorial_with_cache(2999);
}
public static long factorial_with_cache (int n){
if (cache[n] != 0){
return cache[n];
}
cache[n] = n * factorial_with_cache(n - 1);
System.out.println("Factorial(" + n + ") is " + cache[n]);
count++;
return cache[n];
}
}
This will print your calculated fact values.
public class Test2 {
static int count = 0;
static long[] cache = new long[3000];
static {
cache[0] = 1;
}
public static void main(String args[]) {
for (int i = 0; i < 100; i++){
factorial_with_cache(2999);
System.out.println("i[" + i + "] count[" + count +"]");
}
}
public static long factorial_with_cache (int n){
if (cache[n] != 0){
return cache[n];
}
cache[n] = n * factorial_with_cache(n - 1);
count++;
return cache[n];
}
}
This will print count value for each iteration.
I'm relatively new to java and am trying to break my code down as much as possible. This question is really on how to organize methods to work together
My credit card validator works if checkSum() code is written in the validateCreditCard() method. I think it's weird 'cause it works when called by the checkDigitControl() method
I used these sources for the program's logic:
To Check ~ https://www.creditcardvalidator.org/articles/luhn-algorithm
To Generate ~ https://en.wikipedia.org/wiki/Luhn_mod_N_algorithm
Here's my code(I apologize in advance if it's rather clumsy)
public class CreditCards {
public static void main(String[] args) {
long num;
num = genCreditCard();
boolean bool = validateCreditCard(num);
}
// Validity Check
public static boolean validateCreditCard(long card) {
String number = card+"";
String string=null;
int i;
for(i=0; i<number.length()-1; i++) {//Populate new string, leaving out last digit.
string += number.charAt(i)+"";
}
String checkDigit = number.charAt(i)+"";// Stores check digit.
long sum = checkSum(string);// Program works if this line is swapped for the code below(from checkSum)
//**********************************************************************
// int[] digits = new int[number.length()];
// int lastIndex = digits.length-1;
// int position=2; int mod=10;
// int sum=0;
//
// for(int j=lastIndex; j>=0; j--) {// Populate array in REVERSE
// digits[j] = Integer.parseInt(number.charAt(j)+"");
// digits[j] *= ( (position%2 == 0) ? 2: 1 );// x2 every other digit FROM BEHIND
// position++;
//
// digits[j] = ( (digits[j] > 9) ? (digits[j] / mod)+(digits[j] % mod) : digits[j] );//Sums integers of double-digits
// sum += digits[j];
// }
//**********************************************************************
sum *= 9;
string = sum+"";
string = string.charAt(string.length()-1)+"";// Last digit of result.
return (string.equals(checkDigit));
}
public static long genCreditCard() {
String number = "34";// American Express(15 digits) starts with 34 or 37
for(int i=0; i<12; i++)
number += (int)(Math.random() * 10) + "";// Add 12 random digits 4 base.
number += checkDigitControl(number);// Concat the check digit.
System.out.println(number);
return Long.parseLong(number);
}
// Algorithm to calculate the last/checkSum digit.
public static int checkDigitControl(String number) {
int i;
for(i=0; i<5; i++)
++i;
int sum = checkSum(number);
return 10 - sum%10;// Returns number that makes checkSum a multiple of 10.
}
public static int checkSum(String number) {
int[] digits = new int[number.length()];
int lastIndex = digits.length-1;
int position=2; int mod=10;
int sum=0;
for(int j=lastIndex; j>=0; j--) {// Populate array in REVERSE
digits[j] = Integer.parseInt(number.charAt(j)+"");
digits[j] *= ( (position%2 == 0) ? 2: 1 );// x2 every other digit FROM BEHIND
position++;
digits[j] = ( (digits[j] > 9) ? (digits[j] / mod)+(digits[j] % mod) : digits[j] );//Sums integers of double-digits
sum += digits[j];
}
return sum;
}
}
Thx in advance, sorry if this isn't the right format; it's also my 1st Stackoverflow post ¯\_(ツ)_/¯
You are initializing the variable string with null value:
String string=null;
And in the following for you are adding every char of the card number to this string.
for(i=0; i<number.length()-1; i++) {
string += number.charAt(i)+"";
}
But this will result in the variable string to be null + cardnumbers, because you didn't initialize the String string, and the value null is converted to the string "null" (Concatenating null strings in Java)
This will fix you code:
String string = new String();
Note, this code:
for(i=0; i<number.length()-1; i++) {
string += number.charAt(i)+"";
}
can be easily replace by this line that does the same thing:
number = number.substring(0, number.length() -1);
If you switch to this code just pass number to checkSum method
I am writing one java program. Arthur defines a function f(k) to be the number of (p,q) pairs such that:
1< p <= q <= k
p and q are coprimes
p.q=k
I am supposed to write one program for a given integer n and help Arthur find and print the result of (Σ k=1 to n) f(k)
Constraints:
1<=n<=pow(10,9)
For e.g
(Input)Let's say n = 12
For the value of f(k) for 1<=k<=12
For k=6 there is one valid pair (2,3), so f(6) = 1
For k=10 there is one valid pair (2,5), so f(10) = 1
For k=12 there is one valid pair (3,4), so f(12) = 1
For all other 1<=k<=12 the function return 0
So, other final sum is the result of 1+1+1 = 3 (Final output)
Here is my code:
import java.util.Scanner;
class ArthurFunction{
public static boolean areCoPrime(int a, int b){
int max = 0;
boolean flag = true;
if(a>=b)
max = a;
else
max = b;
for(int i=2;i<=max;i++)
if((a%i==0)&&(b%i==0))
flag = false;
return flag;
}
public static void main(String[] args){
Scanner scan = new Scanner(System.in);
int n = scan.nextInt();
int sum = 0;
for(int k = 1;k<=n;k++){
for(int p=2;p<=k;p++){
for(int q=2;q<=k;q++){
if(areCoPrime(p,q)&&(p*q==k)&&(p<=q))
sum+=sum;
}
}
}
System.out.println(sum);
}
}
When I run this code the output should be 3 but I am getting 0 and also unable to find the solution.
You can improve your program by
Making a faster areCoPrime() method
Decrease the number of nested loops in main()
For (1), we know 2 numbers are coprime when their greatest common divisor (GCD) is 1. Their is an efficient method to find GCD called Euclidean algorithm.
For (2), you can remove the 3rd loop, p in the 2nd loop only need to go to sqrt(k)
Refer to my revised code below (Tested: n = pow(10,6) runs less than 2 secs on my PC)
import java.util.Scanner;
class ArthurFunction{
public static boolean areCoPrime(int a, int b){
if (GCD(a,b)==1) return true;
return false;
}
public static int GCD(int a, int b) {
if (b==0) return a;
return GCD(b,a%b);
}
public static void main(String[] args){
Scanner scan = new Scanner(System.in);
int n = scan.nextInt();
int sum = 0;
for(int k=1;k<=n;k++){
for(int p=2;p*p<k;p++){
if(k%p==0) {
int q = k/p;
if (areCoPrime(p,q)) sum++;
}
}
}
System.out.println(sum);
}
}
I am learning Java and discovering that a little bit of knowledge is confusing.
The goal is to write a method that is the equivalent of the n! function. I am using a for loop to multiply a variable declared outside the method. All I get back is 0.
What am I doing wrong?
//
// Complete the method to return the product of
// all the numbers 1 to the parameter n (inclusive)
// # param n
// # return n!
public class MathUtil
{
public int total;
public int product(int n)
{
for (int i = 1; i == n; i ++)
{
total = total * i;
}
return total;
}
}
There is actually a lot of problems in your code:
It does not make sense to make it an instance method.
You have not initialize your total to a reasonable value.
The condition in your for loop is wrong
Method is not given a meaningful name
Messy indentation
(The list keeps growing...)
So here is a slightly improved version
public class MathUtil
{
//
// Complete the method to return the product of
// all the numbers 1 to the parameter n (inclusive)
// # param n
// # return n!
public static int factorial(int n)
{
int total = 1;
for (int i = 1; i <= n; i ++)
{
total = total * i;
}
return total;
}
}
so that you can call it as MathUtil.product(123) instead of some weird new MathUtil().product(123)
Personally I would rather do something like
result = n;
while (--n > 0) {
result *= n;
}
return result;
You are missing the initialization. Now I added the default value to 1. And you also have to change the condition. The for loop has to go on as long as the var i is smaller or equal to n.
public class MathUtil
{
public int total = 1;
public int product(int n)
{
for (int i = 1; i <= n; i ++)
{
total = total * i;
}
return total;
}
}
you didn't initialized total, therefore it's 0. Whenever you multiply 0 with anything, you will get 0 as result.
public int total = 1;
public int product(int n) {
for (int i = 1; i <= n; i++) {
total = total * i;
}
return total;
}
you havent initialized total. It defaults to 0. Then when you multiple anything with total, you get 0 as result