getting permutations

permute-stl.cpp

//
// An example of how to generate permutations
// using STL algorithms library
//
#include <iostream>
#include <algorithm>
using namespace std;

int main () {
  const int N = 8;
  int A[] = { 1, 5, 6, 2, 7, 1, 2, 8 };
  sort(A, A+N);
  do {
    for(int i = 0; i < N; i++)
      cout << A[i] << " ";
    cout << endl;
  } while (next_permutation (A,A+N));
  return 0;
}

permute.cpp

//
// An example of how to generate permutations
// using Heap's algorithm
//
#include <cstdio>
using namespace std;

// an array of stuff to permute
const int N = 8;
int A[N] = { 1, 5, 6, 2, 7, 1, 2, 8 };

void print() {
  for(int i=0; i<N; i++)
    printf("%d ", A[i]);
  printf("\n");
}

int main(int argc, char * argv[])
{
  // make an idx array filled with zero
  int idx[N];
  for(int i=0; i < N; i++)
    idx[i] = 0;

  print();

  // heap's algorithm, iterative version
  for (int i=1; i < N;) {
    if (idx[i] < i) {
      int swap = i % 2 * idx[i];
      int tmp = A[swap];
      A[swap] = A[i];
      A[i] = tmp;
      print();
      idx[i]++;
      i = 1;
    } else {
      idx[i++] = 0;
    }
  }
  return 0;
}

permute.java

//
// An example of how to generate permutations
// using Heap's algorithm (Java version)
//
import java.util.Arrays;

public class Heap {
  private static int A[] = { 1, 5, 6, 2, 7 };
  public static void main(String[] args) {
    // make idx array with zeros
    int[] idx = new int[A.length];
    Arrays.fill(idx, 0);

    System.out.println(Arrays.toString(A));

    // heap's algorithm, iterative
    for (int i = 1; i < A.length;) {
      if (idx[i] < i) {
        int swap = i % 2 * idx[i];
        int tmp = A[swap];
        A[swap] = A[i];
        A[i] = tmp;
        System.out.println(Arrays.toString(A));
        idx[i]++;
        i = 1;
      } else {
        idx[i++] = 0;
      }
    }
  }
}

permute.py

#
# An example of how to generate permutations
# using Heap's algorithm (Python version)
#
def permute(L):
    N = len(L)
    idx = [0 for i in range(N)]
    result = [L]
    i = 1
    while i < N:
        if idx[i] < i:
            L = list(L)
            swap = i % 2 * idx[i]
            L[swap], L[i] = L[i], L[swap]
            result.append(L)
            idx[i] += 1
            i = 1
        else:
            idx[i] = 0
            i += 1
    return result

# 
# How to generate a list of permutations using Python standard library
#
import itertools
itertools.permutations(lis)