LeetCode——two sum

Question

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

Solution

哈希，已知一个数，去哈希表查找另外一个数。

Code

class Solution {
public:
    vector<int> twoSum(vector<int> &numbers, int target) {
        map<int, int> table;
        vector<int> res;
        for (int i = 0; i < numbers.size(); i++) {
            int remain = target - numbers[i];
            if (table.find(remain) != table.end()) {
                int one = i + 1;
                int two = table.find(remain)->second + 1;
                if (one > two) {
                    int tmp = one;
                    one = two;
                    two = tmp;
                }
                res.push_back(one);
                res.push_back(two);
                return res;
            }
            table[numbers[i]] = i;
        }
        return res;
    }
};