1. Two Sum LeetCode

C++ STL map solution O(nlogn). 

class Solution {
	public:
	vector<int> twoSum(vector<int>& nums, int target) {
	map< int ,int > mp;
	vector< int > ans(2, -1);
	for(int i=0; i< (int)nums.size(); i++ ){
	if( mp.find( target - nums[i] ) != mp.end() ){
	return { i, mp[ target - nums[i] ] };
	}
	mp[ nums[i] ] = i;
	}
	return ans;
	}
	};