Description

O(n²)

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

O(n)

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int [] results = new int[2];

        HashMap<Integer, Integer> m = new HashMap<Integer, Integer>();
        
        for(int i = 0; i < nums.length; i++)
        {
            if(m.containsKey(nums[i]))
            {
                results[0] = i;
                results[1] = m.get(nums[i]);
                break;
            }
            else{
                m.put((target-nums[i]), i);
            }
        }

        return results;
    }
}