#include <stdio.h>
#include <stdlib.h>
#include <time.h>

// Random Permutation
//
// Write a complete C program which takes an integer array and produces a 
// random permutation of the array. In other words, the program randomly 
// reshuffles the entries of the array (similar to shuffling a deck
// of cards). The resulting array must be stored in the memory allocated 
// for the original array (i.e., the permutation is done in place).

#define N 10
int main()
{
	int a[N]= {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
	int i;
	
	srand(time(NULL));
	
	// We pick two random array indeces and we swap them. 
	// We repeat 100 times to really make this random.
	// There are better ways to do the shuffling but this one is OK.
	for(i=0; i<100; i++)
	{
		int r1 = rand()%N;
		int r2 = rand()%N;
	
		// swap
		int temp= a[r1];
		a[r1] = a[r2];
		a[r2] = temp;
	}
	
	for(i=0; i<N; i++)
		printf("%d, ", a[i]);
	printf("\n");
	
	system("pause");
}