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Factorial with caching with static int array

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 13831198678126180285189556976955373903170397316439366392298225525658528550411773166953335884059334473358394878461205706165250290371348635931517800720356113203873679301399725840687554463393227601721573232498656280819242922032367667908703698446747042372944385912938442812976579204340368770976791467161792908482026536763476497016597962706920837208377639001547222987372530067858391829660217859289638428364594156664891566396944031170356121274762354507422848113071258383496196034678939603033097637499047300169646331468238450491051510529147169986724755958362486789324705690789582425714662973561230539501202732819906031261484507986168459203695503720787715306962036185816958171315101812071237299383615730698142124734425009998777928314671591890471560274735833304904959453223240212984890196653392856493421129589037623689334983609133572374939825462133789731181451373437595533811597516653047843373551034468875167743673579450500731701049557870779579798365517154053116338596649981357437001475641612713380485162624246015285341187194401439315317685276897783748963573748717156161769574677089322363037849660911158458585633121725465474927244487503626338581145799640164089032772344644035725447994450814858680158855133471471566493328118184865933128900946476171137729637721898436949504508364668715924682335777135513931476001478897301228489756952423900549337170685817482869322924594934553551003036605213030431370211238540513634600045019557208087444634144722209572173742863424856277834965975623123264292792298280478857955478985025157988294085407394460004866920398953072534411602822485072110137246001443714741975414563519594304969324628586261528579942898463434127945755294142551435479172585965738348357120600576683876141492098075828585209276254499589065093789637861306274833094913863894376778010733315584027638295254781954610771181735025318637354022424432317128707664886202509105961484149955116054723079614963020498616978124480963271628142440605710424177963844835527047941127068625126602868360296587251294298750977877916818183056200089076530408509618194827562218441437670451251604136520412562026002566902646513949635716489125951469176102624329367970981707309954931234483752478815193819919046940901995441721784302194857041195090070644484327035189466269961364993448728359341757679578928014056475745993488101416681676935545677586672113973814268569600810283522630702882325818379846373279545389063433426048793378977494110923865060198731023168079278694206856962403099309932476468192292446106625814895181431600107247018896474570181676290139870638357579666677214004824737774431290539343185204668200955800140961796618216776009476171707432009598580600540607745366106990480349004177689104965384412262911661517983201465683450782588737131971506423474040743808999564029154506993562074784937792064798377314289371162177187409391071658827235127282051775532062510098826200386957421213481307419200642164870305628383671047981858132767730852384720717147489707456839716365953949812050321036644546531520598864465617319535112877058774715688947419064131580843908826519916664427749093269298823584351338064696733536570891584395455175134404252585951310232510018865069402485833157299381484590749402629481111706181867189617902727630965072766713218125649095472925555254271796579113386470181227145145782044748230689023360927474548519150294185556719080917603439047213543803560461443641342427106320294937680221742056517608545727954154981431896286464615575574564733158523773515339421141910343038451177576269394257673865595696145764470705694837193543322565755533887878425653323007167374034984753189092864395172089482366791478206807334511797067912797698473565007162069130217730303607114778083832632094745399523891591282708699147685012083622118240243657099361565732179240926631053400186908352669170802498149387797404799372830916093992885059492849249732904712828347430127984696856947346045759045222567855013693926840231677378744507230913510338446973920611359605911891548916357205533551076812967546595355169668436624145148563105200443314135704098338484590507017314148504265121657071624074064576429719944333914132659197510167106279294498294744074169106272133146311875939034291810862931519619247593463572388793752634599383049481842295290543310338170244405184924421525345305394766236107745856279305711691002008912764098229027010250648673458812712892369111259770860752452145178192387601343493641928636582411137977634690746620001816089765370131213375846513299799140007308422976207521653093045456515661082438164698099164737736238987887604321282063792704869736900344337373311421647222149710103632831178455467277094227704168859462141968845732336969092143110178250432445572309805015956983080592707178326499816577452815043403343240119997858835910187898983513330297084001603373363523211048122726398082654521129700828750257789083133267241150542349616716479447911942146684493824985807109624549493196517947945459425200477792599605375618154135498044805373036317551108920542553407043626403888641459832178279343412021431660661847004770522200579839513142002891066188195561545147576726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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.

Trailing Number of Zeros wrong answer on SPOJ (JAVA)

Today I try to solve "Factorial" problem on SPOJ (link) and it looks like easy Trailing Number of Zeros algorithm, but all time I got on SPOJ "Wrong answer".
Algorithm is very easy and works perfect for all tests (from SPOJ, other sources and everything that I created manually), but "Wrong answer" after 0.99 sec...
Here my code:
public static int ZeroCount (int num)
{
int zeros = 0;
for (int i =5; i < num; i*=5)
zeros = zeros + (int)Math.floor(num/i);
return zeros;
}
public static void main(String[] args) throws java.lang.Exception {
Scanner reader = new Scanner(System.in);
int size = reader.nextInt();
while (size > 0) {
System.out.println(Main.ZeroCount(reader.nextInt()));
size--;
}
}
I did it with 1) long vs int; 2) i*=5 vs while loop with Math.pow(a,b) function; 3) Math.floor(c/d) vs simple c/d (because in Java integer dividing works as floor function) and some other simple checks what can go wrong.
Any ideas? Thanks!

Its a really small mistake.
In function ZeroCount, replace i < num by i <= num
public static int ZeroCount (int num)
{
int zeros = 0;
for (int i =5; i <= num; i*=5)
zeros = zeros + (int)Math.floor(num/i);
return zeros;
}

Java with a for loop with in for loop

I am not sure why this isn't working to the questionhave to use a one dimensional integer array to count the number of times each possible sum appears in 36000 rolls.
However my problem is I that keep getting all 0.0 instead of something like 1200000 or 700000.
import java.util.Arrays;
import java.util.Random;
public class StockSim {
public static void main(String args[]) {
double data[] = new double[10];
System.out.println(percentGen());
double percent;
for (int i = 0; i < data.length; i++) {
percent = percentGen();
data[i] = data[i] + (data[i] * percent);
}
}
for (int i = 0; i < data.length; i++) {
System.out.println(data[i]);
}
}
public static double percentGen() {
Random rand = new Random();
return randomNum;
}
}

It is a simple fix, you just forgot to get the actual percentage by dividing the random percentage by one hundred. Substitute your return randomNum by return randomNum/100.
Besides that, I tested your code and it should be working just fine.
I hope that helps!

You also need to move the instantiation of the Random class outside the loop or provide a random seed otherwise the results are not random. For example you could instantiate the Random class and pass it as an argument to percentGen
Random rand= new Random()
System.out.println(percentGen(rand));

Using biginteger to find the sequence of sum of powers

Sum(N) =1^1+2^2+3^3+...+N^N
Using Java,
How would I use BigInteger to find the smallest integer N such that the value of Sum(N) is larger than 10^20?
I'm really stuck,please give me some advice
This is what I have so far:
import java.math.BigInteger;
public class PROJECTV1 {
public static void main(String [] args) {
BigInteger bResult= bigFunctionExample_2();
System.out.println(" => result_got:"+ bResult);
System.out.println(); //newline
}// end_main
public static BigInteger bigFunctionExample_2() {
BigInteger bSum = BigInteger.ZERO;
BigInteger bTmp;
String sSum;
// BigInteger bResult =0;
for (int i=1; ; i++) {
bTmp = BigInteger.valueOf(i);
bTmp = bTmp.pow(i); // i^i
bSum = bSum.add(bTmp); // sum = i^i+ (i-1)^(i-1)+ ....
sSum = bSum.toString();
if ( sSum.length() >21) {
System.out.println("i="+i +" bSum ="+bSum);
break;
}//
}//end_for
return bSum; // result
} // end_bigFunctionExample_2
}

Looking at your code, you have a line bTmp.pow(2). That squares the numbers in your series, but you need to raise bTmp to the bTmp power. Java doesn’t seem to want to take a BigInteger as an argument to pow, but you could replace pow with another for loop.
Also, sSum.length() >30 looks like it will only occur if your sum is greater than or equal to 1029. Is there a reason you convert the number to a string each time through the loop, rather than comparing the number to 1020? Perhaps you could put something like bSum > bMax as the test condition in your for loop, rather than leaving it blank and exiting with a break. Then you could make a new BigInteger bMax and set it to 1020 at the start of your code.
For testing, you could set bMax to something small, like 100, and see if your program gives the correct result. You can calculate the first few steps of the series by hand to check your program.

Here is a clue computing some factorials:
import java.math.*;
public class FactorialBig {
public static BigInteger factorial(BigInteger n) {
if (n.equals(BigInteger.ZERO))
return BigInteger.ONE;
else
return n.multiply(factorial(n.subtract(BigInteger.ONE)));
}
public static void main(String[] args) {
for (int n = 0; n < 20; n++) {
BigInteger f = factorial(new BigInteger(new Integer(n).toString()));
System.out.printf("factorial(%2d) = %20s%n", n, f.toString());
}
}
}
You know you should save the above as a file named "FacotrialBig.java".

what is my error in the sum of power functions?

I was solving this problem6, I dont even know the answer but, when I finished I think that I will get Ok, but my answers fails, 7910956276398901303 this is my answer 1303, can you help me with this error, I dont understand what is wrong my logic , code??, Its just a simple power function
Corrected
this is the correct code
import java.math.BigDecimal;
public class Problema6 {
static BigDecimal sum = BigDecimal.valueOf(0);
static BigDecimal num = BigDecimal.valueOf(0);
public static void main(String args[]) {
int n = 2;
for (int i = 1; i <= 15; i++) {
sum = sum.add(power(i, n));
n++;
}
System.out.println(sum);
String number = sum.toString();
System.out.println(number.substring(number.length() - 4, number.length()));
}
public static BigDecimal power(int x, int y) {
num = BigDecimal.valueOf(x).pow(y).add(BigDecimal.valueOf(y).pow(x));
return num;
}
}

I think the problem is with using Math.pow(...). Switch to BigDecimal.pow(...) to avoid overflows