LeetCode_1.Two Sum

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.

Example:

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

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

return [0, 1]

思路：遍历数组，对每个元素 x，查找（target-x）是否存在于数组中。

代码如下：（参考了九章算法代码 http://www.jiuzhang.com/solutions/two-sum/）

 1 class Solution {
 2 public:
 3     vector<int> twoSum(vector<int>& nums, int target) {
 4
 5         unordered_map<int,int> hash;
 6         vector<int> result(2,-1);
 7
 8         for(int i=0; i<nums.size(); i++)
 9         {
10             if(hash.find(target-nums[i]) != hash.end())
11             {
12                 result[0]=hash[target-nums[i]];
13                 result[1]=i;
14                 return result;
15             }
16
17             hash[nums[i]]=i;
18         }
19
20         return result;
21
22
23     }
24
25
26 };