Problem Description

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

Approach

We can use a Hash Map to store the numbers we have seen so far and their indices. For each number x, we check if target - x exists in the map. If it does, we have found the pair.

Solution

import java.util.HashMap;
import java.util.Map;

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        
        for (int i = 0; i < nums.length; i++) {
            int complement = target - nums[i];
            if (map.containsKey(complement)) {
                return new int[] { map.get(complement), i };
            }
            map.put(nums[i], i);
        }
        
        throw new IllegalArgumentException("No two sum solution");
    }
}