1. Two Sum

Problem:

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, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,

return [0, 1].

Solution:

class Solution {

public:

    vector<int> twoSum(vector<int>& nums, int target) {

        vector<int> res(2);

        int size=nums.size();

        std::map<int,int> hashMap;

        for(int i=0;i<size;i++){

            int curr=target-nums[i];

            if(hashMap.find(curr)!=hashMap.end())

            {

                res[0]=hashMap[curr];

                res[1]=i;return res;

            }

            else

            {

                hashMap[nums[i]]=i;

            }

        }

        return res;     

    }

};