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Two Sum LeetCode Solution

Problem – Two Sum LeetCode Solution

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

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]


  • 2 <= nums.length <= 104
  • -109 <= nums[i] <= 109
  • -109 <= target <= 109
  • Only one valid answer exists.

Two Sum LeetCode Solution in Java

public int[] twoSum(int[] numbers, int target) {
    int[] result = new int[2];
    Map<Integer, Integer> map = new HashMap<Integer, Integer>();
    for (int i = 0; i < numbers.length; i++) {
        if (map.containsKey(target - numbers[i])) {
            result[1] = i;
            result[0] = map.get(target - numbers[i]);
            return result;
        map.put(numbers[i], i);
    return result;

Two Sum LeetCode Solution in Python

class Solution(object):
	def twoSum(self, nums, target):
		buffer_dictionary = {}
		for i in rangenums.__len()):
			if nums[i] in buffer_dictionary:
				return [buffer_dictionary[nums[i]], i] #if a number shows up in the dictionary already that means the 
														#necesarry pair has been iterated on previously
			else: # else is entirely optional
				buffer_dictionary[target - nums[i]] = i 
				# we insert the required number to pair with should it exist later in the list of numbers

Two Sum LeetCode Solution in C++

vector<int> twoSum(vector<int> &numbers, int target)
    //Key is the number and value is its index in the vector.
	unordered_map<int, int> hash;
	vector<int> result;
	for (int i = 0; i < numbers.size(); i++) {
		int numberToFind = target - numbers[i];

            //if numberToFind is found in map, return them
		if (hash.find(numberToFind) != hash.end()) {
                    //+1 because indices are NOT zero based
			result.push_back(hash[numberToFind] + 1);
			result.push_back(i + 1);			
			return result;

            //number was not found. Put it in the map.
		hash[numbers[i]] = i;
	return result;

Two Sum LeetCode Solution in JavaScript

const twoSum = (nums, target) => {
  const map = {};

  for (let i = 0; i < nums.length; i++) {
    const another = target - nums[i];

    if (another in map) {
      return [map[another], i];

    map[nums[i]] = i;

  return null;
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