Leetcode 1. Two Sum

easy, but try hashmap

When you need to keep track of index number, consider hashmap

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