/**

 * Return an array of arrays of size *returnSize.

 * The sizes of the arrays are returned as *columnSizes array.

 * Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().

 */

int com(int n,int k)

{

    int i = ,ans=;

    if(k > n-k) k = n-k;

    for (i = n; i > n - k; i--)

        ans *= i;

    for (i = k; i > ; i--)

        ans /= i;

    return ans;

}

int **ans;

int len;

void back_track(int *last, int last_size, int num, int n, int k)

{

    if(last_size == k)

    {

        int *tmp = (int*)malloc(sizeof(int)*k);

        memcpy(tmp,last,k*sizeof(int));

        ans[len++] = tmp;

        //memcpy(ans[len],last,k*sizeof(int));

        //len ++;

        return;

    }

    if(num > n) return;

    back_track(last,last_size,num+,n,k);

    last[last_size] = num;

    back_track(last,last_size + ,num + ,n,k);

}

int** combine(int n, int k, int** columnSizes, int* returnSize) {

    if(k > n || n *k == )  { *returnSize = ;  return NULL; }

    int size = com(n,k);

    int *cols = (int*)malloc(size*sizeof(int));

    ans = (int**)malloc(size*sizeof(int*));

    len = ;

    for(int i = ; i < size; i ++)

    {

        //ans[i] = (int*)malloc(k*sizeof(int));

        cols[i] = k;

    }

    int *last = (int*)malloc(k*sizeof(int));

    back_track(last,,,n,k);

    *columnSizes = cols;

    *returnSize = len;

    return ans;

}