Oops!

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

#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define MAX(a, b) ((a) > (b) ? (a) : (b))

struct node {
    int index;
    int value;
};

void list_qsort(struct node **list, int size)
{
    struct node *anchor = list[0];
    int i = 1;
    int j = size - 1;
    struct node *tmp = NULL;

    if (size < 2)
        return;

    while (1) {
        while (i < size && list[i]->value <= anchor->value) i++;
        while (j > 0 && list[j]->value > anchor->value) j--;

        if (i > j)
            break;

        tmp = list[i];
        list[i] = list[j];
        list[j] = tmp;
    }

    list[0] = list[j];
    list[j] = anchor;

    list_qsort(list, j);
    list_qsort(list + i, size - i);
}

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int *twoSum(int *nums, int numsSize, int target)
{
    int i, j;
    int *ret = (int *)malloc(2 * sizeof(int));
    struct node **list = (struct node **)malloc(numsSize * sizeof(struct node *));

    if (!ret || !list) {
        printf("malloc failed\n");
        return ret;
    }

    /* initialize node list */
    for (i = 0; i < numsSize; i++) {
        list[i] = (struct node *)malloc(sizeof(struct node));
        if (!list[i]) {
            printf("malloc node failed\n");
            return NULL;
        }
        list[i]->index = i;
        list[i]->value = nums[i];
    }

    /* sort node list */
    list_qsort(list, numsSize);

    /* find target */
    for (i = 0; i < numsSize - 1; i++) {
        for (j = numsSize - 1; j > i; j--) {
            if (list[i]->value + list[j]->value == target) {
                ret[0] = MIN(list[i]->index + 1, list[j]->index + 1);
                ret[1] = MAX(list[i]->index + 1, list[j]->index + 1);

                return ret;
            } else if (list[i]->value + list[j]->value < target) {
                /* stop searching in sorted array */
                break;
            }
        }
    }

    return NULL;
}