1. 两数之和

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

}

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

}

1. 两数之和

原文：https://www.cnblogs.com/cznczai/p/11204606.html