计算两数之和

给定一个整数数组 nums 和一个整数目标值 target，请你在该数组中找出 和为目标值 target  的那 两个 整数，并返回它们的数组下标。

你可以假设每种输入只会对应一个答案。但是，数组中同一个元素在答案里不能重复出现。

示例 1：

输入：nums = [2,7,11,15], target = 9
输出：[0,1]
解释：因为 nums[0] + nums[1] == 9 ，返回 [0, 1] 

Java实现

public static void main(String[] args){
        int nums[] = {1,2,3,4,5};
        int nums2[] = {2,2};
        int targ = 8;
        int targ2 = 4;
        System.out.println(Arrays.toString(twoSum(nums,targ)));//[2, 4]
        System.out.println(Arrays.toString(twoSum2(nums2,targ2)));//[0,1]
}
    //方法1
public static  int[] twoSum(int[] nums, int target) {
        int res[] = new int[2];
        for (int i=0;i<nums.length;i++){
            for (int j=i+1;j<nums.length;j++){
                if (nums[i]+nums[j] == target){
                    res[0] = i;
                    res[1] = j;
                    break;
                }
            }
        }
        return res;
}
   //方法2  有点问题输入为[3,3]测试错误
public static  int[] twoSum2(int[] nums, int target) {
        int res[] = new int[2];
        Map<Integer,Integer> map = new HashMap();

        for (int j=0;j<nums.length;j++){
            int tmep = target-nums[j];
            if (map.containsKey(tmep)){
                res[0] = (int) map.get(tmep);//get()获取到temp的value值
                res[1] = j;
            }
            //将数组存入一个map对象，key=数组元素，value=元素下标
            map.put(nums[j],j);
        }
        return res;
}

JS实现

let n = [1,3,5,7];
let tar = 10;

//方法1
let twoSum = function(nums,target){
  let res = new Array();
  for(let i=0;i<nums.length;i++){
    for(let j = i+1;j<nums.length;j++){
      if(nums[i]+nums[j] === target){
          res.push(i,j);
          return res;
      }
    }
  }
  
}
console.log(twoSum(n,tar));//[ 1, 3 ]

let n2 = [3,3];
let tar2 = 6;

//方法2
let twoSum2 = function(nums,target){
  let map = new Map();
  for(let j in nums){
      let temp = target-nums[j];
      if (map.has(temp)) {
        return [j,map.get(temp)];
      }
      map.set(num[j],j);
  }
  
}

console.log(twoSum(n2,tar2));//[ 0, 1 ]