1. 两数之和 - 力扣（LeetCode）

一、Java

import java.util.HashMap;

class Solution {
    public int[] twoSum(int[] nums, int target) { //返回数组
        HashMap<Integer, Integer> map = new HashMap<>(); //键：元素值；值：元素索引
        for (int i = 0; i < nums.length; i++) {
            if (map.containsKey(target - nums[i]))
                return new int[]{map.get(target - nums[i]), i};
            else
                map.put(nums[i], i);
        }
        return null;
    }
}

二、C++

#include <vector>
#include <unordered_map>
using namespace std;
class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int, int> m; //unordered_map：哈希映射
        for (int i = 0; i < nums.size(); i++) {
            if (m.find(target - nums[i]) != 0)
                return {m[target - nums[i]], i};
            else
                m.insert({nums[i], i});
        }
        return {};
    }
};

三、Python

from typing import List


class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        m = {}
        for i in range(len(nums)):
            if target - nums[i] in m:
                return [m[target - nums[i]], i]
            else:
                m[nums[i]] = i

四、JavaScript

var twoSum = function(nums, target) {
    let m = new Map();
    for (let i = 0; i < nums.length; i++) {
        if ( m.has(target - nums[i]))
            return [m.get(target - nums[i]), i];
        else
            m.set(nums[i], i); 
    }
};

五、Go

package main

func twoSum(nums []int, target int) []int {
	m := make(map[int]int)
	for i := 0; i < len(nums); i++ {
		if idx, ok := m[target-nums[i]]; ok {
			return []int{idx, i}
		} else {
			m[nums[i]] = i
		}
	}
	return []int{}
}