1_TwoSum.cpp

/*
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.
*/

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> res;
        unordered_map<int, int> hash;
        
        for(int i = 0; i < nums.size(); i++){
            int Num = target - nums[i];
            if(hash.find(Num) != hash.end()){
                res.push_back(i);
                res.push_back(hash[Num]);
                sort(res.begin(), res.end());
                return res;
            }
            hash[nums[i]] = i;
        }
        return res;
    }
};