[leetcode] 1.Two Sum

Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution.

Example:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Logic

Iterate nums array, for each element nums[i] in nums array, check if the hashmap stores target-nums[i].

Time Complexity

O(n)

Space Complexity

O(n)

Code

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        for(int i=0; i<nums.length; i++){
            if(!map.containsKey(target-nums[i]))
                map.put(nums[i], i);
            else{
                int[] re = new int[2];
                re[0] = map.get(target-nums[i]);
                re[1] = i;
                return re;
            }
        }
        return new int[2];
        
    }
}