twoSum.cpp

/**
 ** LeetCode NO.1
 ** 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].
 **/

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> answer;
        map<int, int> hash;
        int remain;
        for (int i = 0; i < nums.size(); i++) {
            remain = target - nums[i];
            if (hash.find(remain) != hash.end()) {
                answer.push_back(hash[remain]);
                answer.push_back(i);
                return answer;
            } else {
                hash.insert(make_pair(nums[i], i));
            }
        }
        return answer;
    }
};