Two Sum
Desicription
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:
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 Given nums = [2, 7, 11, 15], target = 9, Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].

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