Permutations
Permutations
You are encouraged to solve this task according to the task description, using any language you may know.
You are encouraged to solve this task according to the task description, using any language you may know.
Write a program which generates the all permutations of n different objects. (Practically numerals!)
Java
Using the code of Michael Gilleland. <lang java> package hu.pj.alg.permut.cl;
public class PermutationGenerator {
private int[] array; private int firstNum; private boolean firstReady = false;
public PermutationGenerator(int n, int firstNum_) { if (n < 1) { throw new IllegalArgumentException("The n must be min. 1"); } firstNum = firstNum_; array = new int[n]; reset(); }
public void reset() { for (int i = 0; i < array.length; i++) { array[i] = i + firstNum; } firstReady = false; }
public boolean hasMore() { boolean end = firstReady; for (int i = 1; i < array.length; i++) { end = end && array[i] < array[i-1]; } return !end; }
public int[] getNext() {
if (!firstReady) { firstReady = true; return array; }
int temp; int j = array.length - 2; int k = array.length - 1;
// Find largest index j with a[j] < a[j+1]
for (;array[j] > array[j+1]; j--);
// Find index k such that a[k] is smallest integer // greater than a[j] to the right of a[j]
for (;array[j] > array[k]; k--);
// Interchange a[j] and a[k]
temp = array[k]; array[k] = array[j]; array[j] = temp;
// Put tail end of permutation after jth position in increasing order
int r = array.length - 1; int s = j + 1;
while (r > s) { temp = array[s]; array[s++] = array[r]; array[r--] = temp; }
return array; } // getNext()
// For testing of the PermutationGenerator class public static void main(String[] args) { PermutationGenerator pg = new PermutationGenerator(3, 1);
while (pg.hasMore()) { int[] temp = pg.getNext(); for (int i = 0; i < temp.length; i++) { System.out.print(temp[i] + " "); } System.out.println(); } }
} // class </lang>
If I tested the program for n=3 with beginning 1, I got this output:
1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1