leetcode 1: Two Sum

Use a unordered map to save all visited number. While scan the array, find out whether target-nums[i] is already visited.

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