[leetcode 1] Two Sum

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9

Output: index1=1, index2=2

思路1：排序，在夹逼。时间复杂度高一些

思路2：用哈希表储存变量，健为number的值，值为其index。下面的代码实现是思路2

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