Problem Statement​

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

Video Explanation​

Watch

Approach​

To solve this problem, we can use a hash map to store the numbers and their indices. As we iterate through the list, we check if the complement (target - current number) exists in the hash map.

Steps:​

1. Initialize:

   • Create an empty hash map.

2. Iterate:

   • For each number in nums, calculate its complement.
   • Check if the complement exists in the hash map.
   • If it exists, return the indices.
   • Otherwise, add the current number and its index to the hash map.

3. Return:

   • If no solution is found, return an empty list.

Solutions​

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int, int> numMap;
        for (int i = 0; i < nums.size(); i++) {
            int complement = target - nums[i];
            if (numMap.count(complement)) {
                return {numMap[complement], i};
            }
            numMap[nums[i]] = i;
        }
        return {};
    }
};

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);
        }
        return new int[] {};
    }
}

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        num_map = {}
        for i, num in enumerate(nums):
            complement = target - num
            if complement in num_map:
                return [num_map[complement], i]
            num_map[num] = i

var twoSum = function(nums, target) {
    const map = new Map();
    for (let i = 0; i < nums.length; i++) {
        const complement = target - nums[i];
        if (map.has(complement)) {
            return [map.get(complement), i];
        }
        map.set(nums[i], i);
    }
    return [];
};