leetcode1

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].

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

代码：

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> ret(2,-1);
        unordered_map<int, int> m;    //value->index map
        for(int i = 0; i < nums.size(); i ++)
        {
            if(m.find(target-nums[i])== m.end())  //target-numbers[i] appeared 
                m[nums[i]]=i;
            else
           {
                ret[0] = m[target-nums[i]]; 
                ret[1] = i;
            }
        }
    return ret;
    }
    
};