1. 两数之和

此题是可以理解为查找、添加类题目，是典型的hash做法，可以使用uthash来实现，代码如下：

typedef struct {
    int key;
    int val;
    UT_hash_handle hh;
} my_hash;
my_hash *g_user;

int* twoSum(int* nums, int numsSize, int target, int* returnSize){
    int i;
    g_user = NULL;
    my_hash *tmp = NULL;
    int *res = malloc(2 * sizeof(int));
    *returnSize = 2;
    for(i = 0; i<numsSize; i++) {
        int to_find = target - nums[i];
        HASH_FIND_INT(g_user, &to_find, tmp);
        if(tmp == NULL) {
            tmp = malloc(sizeof(my_hash));
            tmp->key = nums[i];
            tmp->val = i;
            HASH_ADD_INT(g_user, key, tmp);
        } else {

            res[0] = tmp->val;
            res[1]= i;
            break;
        }
    }
    return res;
}