Question

I am using a recursive algorithm to list all possible permutations of elements of an array p = {1,2,3}. Following is the simple recursive implementation I am using:

void swap(int x, int y){
    int temp = array[x];
    array[x]=array[y];
    array[y]=temp;    
    return;
}

void printArray(int size){
    int i;

    for (i=0;i<size;i++)
        printf("%d ", array[i]);

    printf("\n");    
    return;
}

void permute(int k,int size){
    int i;

    if (k==0)
        printArray(size);
    else{
        for (i=k-1;i>=0;i--){
            swap(i,k-1);
            permute(k-1,size);
            swap(i,k-1);
        }
    }    
    return;
}

The problem is instead of printing them I want to add every permutation to a 2D array. Currently, I am printing the permutations to a file and then reading it to a 2D array, but I think there should be a better way to do this.

Answer 1

declaring these as global:

int **resultArray;
resultArray = malloc( (n!) * sizeof(int *));    // n! : factorial of n
for(i=0; i<(n!); i++)
    resultArray[i] = malloc(size * sizeof(int));
int index = 0;

this to fill in the 2 dimensional array:

void addToArray(int size){
    int i;
    for(i=0 ; i<size ; i++)
        resultArray[index][i] = array[i];
    index++;
}