Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0
 
, 1].

思路：1.枚舉判斷每個元素與另一個元素之和是否等於目標值
　　　2.哈希查找，將所有元素存入hashmap中，目標值減去每個元素等於某個值。看這個值是否等於剩下某個元素。

 1 int* twoSum(int* nums, int numsSize, int target) {
 2     int *a = (int *)malloc(2*sizeof(int));
 3     int num = 0;
 4     for(int i=0;i<numsSize;i++){
 5         for(int j=i+1;j<numsSize;j++){
 6             if
 
(nums[i]+nums[j]==target){
 7                 a[0] = i;
 8                 a[1] = j;
 9             }
10         }
11     }
12     return a;
13     
14 }

LeetCode 1. Two Sum