With n=5 and k=3 the following loop will do it
List<String> l=new ArrayList<String>();
l.add("A");l.add("B");l.add("C");l.add("D");l.add("E");
int broadcastSize = (int) Math.pow(2, l.size());
for (int i = 1; i < broadcastSize; i++) {
StringBuffer buffer = new StringBuffer(50);
int mask = i;
int j = 0;
int size=0;
System.out.println();
while (mask > 0) {
if ((mask & 1) == 1) {
System.out.println(".. "+mask);
buffer.append(l.get(j));
if (++size>3){
buffer = new StringBuffer(50);
break;
}
}
System.out.println(" "+mask);
mask >>= 1;
j++;
}
if (buffer.length()>0)
System.out.println(buffer.toString());
}
but it's not efficient I would like to do it with Banker's sequence and thus explore first singletons, then pairs, then 3-tuple and stop.
I did not find a way do that, but at least this loop should be more efficient:
List<String> l=new ArrayList<String>();
l.add("A");l.add("B");l.add("C");l.add("D");l.add("E");
int broadcastSize = (int) Math.pow(2, l.size());
for (int i = 1; i < broadcastSize; i++) {
StringBuffer buffer = new StringBuffer(50);
int mask = i;
int j = 0;
if (StringUtils.countMatches(Integer.toBinaryString(i), "1") < 4){
while (mask > 0) {
if ((mask & 1) == 1) {
buffer.append(l.get(j));
}
mask >>= 1;
j++;
}
if (buffer.length()>0)
System.out.println(buffer.toString());
}
}
there is also: but k embedded loops looks ugly
//singleton
for (int i = 0; i < l.size(); i++) {
System.out.println(l.get(i));
}
//pairs
for (int i = 0; i < l.size(); i++) {
for (int j = i+1; j < l.size(); j++) {
System.out.println(l.get(i)+l.get(j));
}
}
//3-tuple
for (int i = 0; i < l.size(); i++) {
for (int j = i+1; j < l.size(); j++) {
for (int k = j+1; k < l.size(); k++) {
System.out.println(l.get(i)+l.get(j)+l.get(k));
}
}
}
//...
// k-tuple
This technique is called Gosper's hack. It only works for n <= 32 because it uses the bits of an int, but you can increase it to 64 if you use a long.
int nextCombo(int x) {
// moves to the next combination with the same number of 1 bits
int u = x & (-x);
int v = u + x;
return v + (((v ^ x) / u) >> 2);
}
...
for (int x = (1 << k) - 1; (x >>> n) == 0; x = nextCombo(x)) {
System.out.println(Integer.toBinaryString(x));
}
For n = 5 and k = 3, this prints
111
1011
1101
1110
10011
10101
10110
11001
11010
11100
exactly as you'd expect.
this should be the most efficient way, even if k embedded loops looks ugly
//singleton
for (int i = 0; i < l.size(); i++) {
System.out.println(l.get(i));
}
//pairs
for (int i = 0; i < l.size(); i++) {
for (int j = i+1; j < l.size(); j++) {
System.out.println(l.get(i)+l.get(j));
}
}
//3-tuple
for (int i = 0; i < l.size(); i++) {
for (int j = i+1; j < l.size(); j++) {
for (int k = j+1; k < l.size(); k++) {
System.out.println(l.get(i)+l.get(j)+l.get(k));
}
}
}
// ...
//k-tuple
Apache commons has iterators for subsets of size k, and for permutations.
Here is an iterator that iterates through 1-k tuples of an n-tuple, that combines the two:
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import org.apache.commons.collections4.iterators.PermutationIterator;
import org.apache.commons.math3.util.Combinations;
public class AllTuplesUpToKIterator implements Iterator<List<Integer>> {
private Iterator<int[]> combinationIterator;
private PermutationIterator<Integer> permutationIterator;
int i;
int k;
int n;
public AllTuplesUpToKIterator(int n, int k) {
this.i = 1;
this.k = k;
this.n = n;
combinationIterator = new Combinations(n, 1).iterator();
permutationIterator = new PermutationIterator<Integer>(intArrayToIntegerList(combinationIterator.next()));
}
#Override
public boolean hasNext() {
if (permutationIterator.hasNext()) {
return true;
} else if (combinationIterator.hasNext()) {
return true;
} else if (i<k) {
return true;
} else {
return false;
}
}
#Override
public List<Integer> next() {
if (!permutationIterator.hasNext()) {
if (!combinationIterator.hasNext()) {
i++;
combinationIterator = new Combinations(n, i).iterator();
}
permutationIterator = new PermutationIterator<Integer>(intArrayToIntegerList(combinationIterator.next()));
}
return permutationIterator.next();
}
#Override
public void remove() {
// TODO Auto-generated method stub
}
public static List<Integer> intArrayToIntegerList(int[] arr) {
List<Integer> result = new ArrayList<Integer>();
for (int i=0; i< arr.length; i++) {
result.add(arr[i]);
}
return result;
}
public static void main(String[] args) {
int n = 4;
int k = 2;
for (AllTuplesUpToKIterator iter= new AllTuplesUpToKIterator(n, k); iter.hasNext();) {
System.out.println(iter.next());
}
}
}
Related
So I'm trying to create Bubble and Selection sort and this is the code I have so far.
package club.westcs.javabasics;
import java.util.ArrayList;
import java.util.Collections;
public class SortsRunner {
public static void BubbleSort(ArrayList<Integer> nums) {
int n = nums.size();
for (int i = 0; i < n; i++) {
boolean swapped = false;
for (int j = 0; j < n-1; j++) {
if (nums.get(j) > nums.get(j + 1)) {
int temp = nums.get(j);
nums.set(j, nums.get(j + 1));
nums.set(j + 1, temp);
swapped = true;
}
}
if (!swapped) {
break;
}
}
}
public static void SelectionSort(ArrayList<Integer> nums) {
int n = nums.size();
for (int i = 0; i < n-1; i++)
{
int min_idx = i;
for (int j = i+1; j < n; j++)
if (nums.get(j) < nums.get(min_idx))
min_idx = j;
int temp = nums.get(min_idx);
nums.set(j, nums.get(j+1)) = nums.set(i);
nums.set(i, min_idx) = temp;
}
}
public static void printArrayList(ArrayList<Integer> nums) {
for(int i = 0; i < nums.size(); i++) {
System.out.println(nums.get(i) + " ");
}
System.out.println();
}
public static ArrayList<Integer> makeRandomArrayList() {
ArrayList<Integer> nums = new ArrayList<>();
for(int i = 0; i < (int)(Math.random() * 11) + 5; i++) {
nums.add((int)(Math.random() * 100));
}
return nums;
}
public static void main(String[] args) {
printArrayList(makeRandomArrayList());
}
}
My selection sort is erroring for nums.set(j, nums.get(j+1)) = nums.set(i); and nums.set(i, min_idx) = temp; I want this portion of the code to swap the minimum element with the first element. I'm not sure how to do it correctly with the ArrayList stuff. Could someone give me some tips?
You are getting a compilation error because it is impossible to use '=' operator for void functions (such as nums.set(j, nums.get(j+1))). Setters are always void and you cannot assign smth to nothing!
The signature of ArrayList setter looks like:
public E set(int index, E element)
where first parameter is index of the array (0, 2, 3 ... N), second is a value you want to set under this index.
By the way your selection sort looks strange.
Try this code:
public static void doSelectionSort(ArrayList<Integer> arr) {
for (int i = 0; i < arr.size(); i++) {
// find position of smallest num between (i + 1)th element and last element
int pos = i;
for (int j = i; j < arr.size(); j++) {
if (arr.get(j) < arr.get(pos))
pos = j;
}
// Swap min (smallest num) to current position on array
int min = arr.get(pos);
arr.set(pos, arr.get(i));
arr.set(i, min);
printOut(i + 1, arr);
}
}
Given the number n, not exceeding 10, and a matrix of size n × n.
Check whether this matrix is symmetric in relation to the main diagonal. Output the word “YES”, if it is symmetric and the word “NO” otherwise.
This is my code, it unfortunately does not work. Please, explain to me how to do it correctly :)
public class Main { public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n= scanner.nextInt();
int[][] number = new int[n][n];
boolean ismatch = false;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
number[i][j] = scanner.nextInt();
}
}
int unevenchecker = (n% 2);
if (unevenchecker != 0) {
for (int k = 0; k < number.length - 1; k++) {
for (int l = 0; l < number.length - 1; l++) {
if (number[k][l] == number[l][k]) {
ismatch = true;
}
}
}
if (ismatch) {
System.out.print("YES");
}
} else {
System.out.print("NO");
}
}
}
The matrix is not symmetric if you find at least 1 symmetric couple where the 2 parts are not equal, so instead of checking for equality inside the loop, check for inequality:
ismatch = true;
for (int k = 0; k < number.length - 1; k++) {
for (int l = 0; l < number.length - 1; l++) {
if (number[k][l] != number[l][k]) {
ismatch = false;
break;
}
}
}
public class Main {
static boolean isSymmetric(int mat[][], int size) {
for (int i = 0; i < size; i++)
for (int j = i + 1; j < size - i; j++)
if (mat[i][j] != mat[j][i])
return false;
return true;
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n= scanner.nextInt();
int[][] number = new int[n][n];
boolean ismatch = false;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
number[i][j] = scanner.nextInt();
}
}
if (isSymmetric(number, n)) {
System.out.print("YES");
} else {
System.out.print("NO");
}
}
}
Notice that the nested loop into isSymmetric starts from j = i + 1, for not checking twice same condition.
currently I am trying to implement a CPLEX exact solution for the Asymmetric Capacitated Vehicle Routing Problem with the MTZ sub-tour elimination constraints.
My problems occurs when I try to implement Lazy Constraint Callbacks. More specifically I get a null pointer exception. There are almost no tutorials for implementing callbacks, so your help will be deeply appreciated.
This is my code:
CVRP class
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import ilog.concert.*;
import ilog.cplex.*;
public class ACVRP {
// euclidean distance method
public static double distance(int x1, int y1, int x2, int y2) {
return Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
}
public static void solveModel() {
int n = 32; // number of customers
int k = 5; // number of vehicles
int c = 100; // capacity of vehicles
int datacoords[][] = new int[n][2];
double[][] node = new double[n][n]; // dissimilarity matrix
int[] demand = new int[n]; // demand of every customer
try {
// load matrixes
FileReader frd = new FileReader("demands.txt");
FileReader frcoords = new FileReader("coords.txt");
BufferedReader brd = new BufferedReader(frd);
BufferedReader brcoords = new BufferedReader(frcoords);
String str;
int counter = 0;
while ((str = brd.readLine()) != null) {
String[] splitStr = str.trim().split("\\s+");
demand[counter] = Integer.parseInt(splitStr[1]);
counter++;
}
counter = 0;
while ((str = brcoords.readLine()) != null) {
String[] splitStr = str.trim().split("\\s+");
datacoords[counter][0] = Integer.parseInt(splitStr[1]);
datacoords[counter][1] = Integer.parseInt(splitStr[2]);
counter++;
}
for(int i = 0; i < n; i++){
for(int j = 0; j < n; j++){
node[i][j] = distance(datacoords[i][0],datacoords[i][1],datacoords[j][0],datacoords[j][1]);
// if (i == j ){
// node[i][j] = 99999999;
// }
}
}
brd.close();
brcoords.close();
IloCplex cplex = new IloCplex();
// variables
IloIntVar[][] x = new IloIntVar[n][];
for (int i = 0; i < n; i++) {
x[i] = cplex.boolVarArray(n);
for (int j = 0; j < n; j++) {
x[i][j].setName("x." + i + "." + j );
}
}
// mtz variables
IloNumVar[] u = cplex.numVarArray(n, 0, Double.MAX_VALUE);
for (int j = 0; j < n; j++) {
u[j].setName("u." + j);
}
//objective
IloLinearNumExpr conObj = cplex.linearNumExpr();
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if ( i != j ){
conObj.addTerm(node[i][j], x[i][j]) ;
}
}
}
cplex.addMinimize(conObj);
// constraints
for (int i = 1; i < n; i++) {
IloLinearNumExpr equation1 = cplex.linearNumExpr();
for (int j = 0; j < n; j++) {
if (i!=j) {
equation1.addTerm(1.0, x[i][j]);
}
}
cplex.addEq(equation1, 1.0);
}
for (int j = 1; j < n; j++) {
IloLinearNumExpr equation2 = cplex.linearNumExpr();
for (int i = 0; i < n; i++) {
if (i!=j) {
equation2.addTerm(1.0, x[i][j]);
}
}
cplex.addEq(equation2, 1.0);
}
IloLinearNumExpr equation3 = cplex.linearNumExpr();
for (int i = 1; i < n; i++) {
equation3.addTerm(1.0, x[i][0]);
}
cplex.addEq(equation3, k);
IloLinearNumExpr equation4 = cplex.linearNumExpr();
for (int j = 1; j < n; j++) {
equation4.addTerm(1.0, x[0][j]);
}
cplex.addEq(equation4, k);
cplex.use(new LazyContstraintMTZ(n, c, demand, x, u, cplex));
//parameters
//cplex.setParam(IloCplex.Param.TimeLimit,50);
//cplex.setParam(IloCplex.Param.Preprocessing.Reduce, 0);
// cplex.setParam(IloCplex.Param.RootAlgorithm, IloCplex.Algorithm.Primal);
// solve model
cplex.solve();
cplex.exportModel("model.lp");
System.out.println(cplex.getBestObjValue());
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (i != j) {
if (cplex.getValue(x[i][j]) != 0) {
System.out.println("name: " + x[i][j].getName() + " value: " + cplex.getValue(x[i][j]));
}
}
}
}
// end
cplex.end();
} catch (IloException | NumberFormatException | IOException exc) {
exc.printStackTrace();
}
}
}
class for lazy constraint :
import ilog.concert.*;
import ilog.cplex.*;
public class LazyContstraintMTZ extends IloCplex.LazyConstraintCallback {
int n; // number of customers
int c; // capacity of vehicles
int[] demand; // demand of every customer
IloIntVar[][] x;
IloNumVar[] u;
IloCplex cplex;
IloRange[] rng;
//constructor
LazyContstraintMTZ(int n, int c, int[] demand, IloIntVar[][] x, IloNumVar[] u, IloCplex cplex){
this.n = n;
this.c = c;
this.demand = demand;
this.x = x;
this.u = u;
this.cplex = cplex;
}
protected void main() throws IloException {
// Get the current x solution
// double[][] sol = new double[n][n];
// for (int i = 0; i < n; i++) {
// for (int j = 0; j < n; j++) {
// sol[i][j] = cplex.getValue(x[i][j]);
// }
// }
for (int i = 1; i < n; i++) {
for (int j = 1; j < n; j++) {
if (i!=j && demand[i]+demand[j]<=c){
IloLinearNumExpr equation5 = cplex.linearNumExpr();
equation5.addTerm(1.0, u[i]);
equation5.addTerm(-1.0, u[j]);
equation5.addTerm(c, x[i][j]);
rng[i].setExpr(equation5);
rng[i].setBounds(Double.MIN_VALUE, c-demand[j]);
cplex.addLazyConstraint(rng[i]);
}
}
}
for (int i = 1; i < n; i++) {
IloLinearNumExpr equation6 = cplex.linearNumExpr();
equation6.addTerm(1.0, u[i]);
rng[i].setExpr(equation6);
rng[i].setBounds(demand[i], c);
cplex.addLazyConstraint(rng[i]);
}
}
}
As far as I can tell, rng is never initialized in your callback class. So it is always null and as soon as you attempt to set an element in it, you will get that NullPointerException.
Note that you don't even need that array. Instead of
rng[i].setExpr(equation5);
rng[i].setBounds(Double.MIN_VALUE, c-demand[j]);
cplex.addLazyConstraint(rng[i]);
you can just write
IloRange rng = cplex.range(Double.MIN_VALUE, equation5, c - demand[j]);
cplex.addLazyConstraint(rng);
(and similarly for equation6).
Also note that Double.MIN_VALUE is likely not what you want. This gives the smallest representable number larger than 0. I guess what you want is Double.NEGATIVE_INFINITY to specify a range without lower bound. In that case you could also just write
IloRange rng = cplex.le(equation5, c - demand[j]);
I have just written up this code an have been trying for ages to try and find out why it is not printing the sorted list. It is running and there are no bugs, except it just does not print out the sorted list. Can you please help me find whats wrong?
public class Merging {
public static void main(String[] args) {
int[] a = new int[10];
populate(a);
printA(a);
a = merge_sort(a);
printA(a);
}
public static int[] merge_sort(int[] B) {
if (B.length <= 1) {
return B;
}
int midpoint = B.length / 2;
int[] left = new int[midpoint];
int[] right= new int[B.length-midpoint];
int[] result;
for (int i = 0; i < midpoint; i++) {
left[i] = B[i];
}
int x = 0;
for (int j = midpoint; j < B.length; j++) {
if (x < right.length) {
right[x] = B[j];
x++;
}
}
left = merge_sort(left);
right = merge_sort(right);
result = merge(left, right);
return result;
}
public static int[] merge(int[] left, int[] right) {
int lengthResult = left.length + right.length;
int[] result = new int[lengthResult];
int indexL = 0;
int indexR = 0;
int indexRes = 0;
while (indexL < left.length || indexR < right.length) {
if (indexL < left.length && indexR < right.length) {
if (left[indexL] <= right[indexR]) {
result[indexRes] = left[indexL];
indexL++;
indexRes++;
} else {
result[indexRes] = right[indexR];
indexR++;
indexRes++;
}
} else if (indexL < left.length) {
result[indexRes] = left[indexL];
indexL++;
indexRes++;
}
}
return result;
}
public static void printA(int[] B) {
for (int i = 0; i < B.length; i++) {
System.out.print(B[i] + " ");
}
}
public static int[] populate(int[] B) {
for (int i = 0; i < B.length; i++) {
B[i] = (int) (Math.random() * 100);
}
return B;
}
}
imagine the case in your loop, where indexL < left.length == false but indexR < right.length == true, you never increase indexR and the loop will never terminate
I have a method transpose in class Matice. When i apply this method on my m2.matice i can see during debugging that my matrix is being transposed, but when i print m2 i get the same matrix as before.
public class Main {
public static void main(String[] args) {
Matice m1 = new Matice(5);
m1.matrixFill(0, 5);
m1.matrixPrint();
Matice m2 = new Matice(3);
m2.matrixFill(-5, 10);
m2.matrixPrint();
m2.transpose();
m2.matrixPrint();
}
}
package matice;
/**
*
* #author Adam Rychter
*/
public class Matice {
int[][] matice;
private int n;
public Matice(int n) {
this.n = n;
if(n > 0) {
matice = new int[n][n];
}
}
public void matrixPrint(){
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
System.out.format("%5d", matice[i][j]);
}
System.out.println("");
}
System.out.println("");
}
public void matrixFill(int a, int b){
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
matice[i][j] = (int) (Math.random() * (a + b + 1) - a);
}
}
}
public void transpose(){
int tmp;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
tmp = matice[i][j];
matice[i][j] = matice[j][i];
matice[j][i] = tmp;
}
}
}
}
Your problem is that you're transposing each element twice ! once when i=row, j=col, and once when i=col, j=row, with the net effect of leaving the matrix as it was. The easiest way I see to fix it is do the swap only if i>j (and then test to make sure :) this is a suggestion, not working code :)
Note that j goes from i to n, not 1 to n; also note need for two tmp variables.
public void transpose(){
int tmp1, tmp2;
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
tmp1 = matice[i][j];
tmp2 = matice[j][i];
matice[i][j] = tmp2;
matice[j][i] = tmp1;
}
}
Like this, maybe:
public void transpose(){
Matice mL = new Matice(n);
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
mL.matice[i][j] = matice[j][i];
}
}
matice = mL.matice;
}
See alternate, more efficient answer above.
public void transpose(){
int tmp;
for (int i = 0; i < n; i++) {
for (int j = i+1; j < n; j++) {
tmp = matice[i][j];
matice[i][j] = matice[j][i];
matice[j][i] = tmp;
}
}
}