leetcode1-两数之和

两数之和

• 暴力遍历

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;
    }
}

• 哈希

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