Blind 75 Must Do Leetcode - Two sum

https://leetcode.com/list/xi4ci4ig/

Favorite - LeetCode

1. Brute Force - O(N^2)

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int [] result = new int[2];
        
        //1. for문 2개
        for(int i =0; i<nums.length-1;i++){
            for(int j = i+1;j<nums.length;j++){
                if(nums[i]+nums[j] == target) {
                    result[0] = i;
                    result[1] = j;
                    break;
                }
            }
        }
    
        return result;
    }
}

 

 

 

 

2. using hashmap ( O(N) )

class Solution {
    public int[] twoSum(int[] nums, int target) {
        HashMap<Integer, Integer> map = new HashMap<>();
        
        for(int i =0; i<nums.length;i++){
            if(map.containsKey(nums[i])){
                int first = map.get(nums[i]);
                return new int[] {first, i};
            }else {
                map.put(target-nums[i], i);
            }
        }
        return new int[2];
    }
}