1. 两数之和

两数之和

方法一：暴力两层for循环

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

方法二：哈希表

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