Two Sum

easy 原题链接：https://leetcode.com/problems/two-sum/

Two Sum

原题链接：https://leetcode.com/problems/two-sum/

描述

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

例子

Input: nums = [2,7,11,15], target = 9 Output: [0,1]

Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Input: nums = [3,2,4], target = 6

Output: [1,2]

约束

• 2 <= nums.length <= 105

• -109 <= nums[i] <= 109

• -109 <= target <= 109

• Only one valid answer exists.

解法一

解法二

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

总结