leetcode 1---Two Sum 数组 哈希

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

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

Example:
Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

最笨的方法：

public class Solution {    public int[] twoSum(int[] nums, int target) {        int [] res={1,2};        for(int i=0;i<nums.length;i++){           int temp=nums[i];           for(int j=i+1;j<nums.length;j++){               if(temp+nums[j]==target){                 res[0]=i; res[1]=j;                  }           }       }       return res;    }}

较好的是使用hash:

public class Solution {    public int[] twoSum(int[] nums, int target) {       int [] res=new int[2];       Map<Integer, Integer> m = new HashMap<>();        for(int i=0;i<nums.length;i++){            if(m.get(target-nums[i])!=null){                res[0]=i;                res[1]=m.get(target-nums[i]);                return res;                }            m.put(nums[i],i);        }        return res;    }}