Two Sum Leetcode Solution

In this post, we are going to solve the Two Sum Leetcode Solution problem of Leetcode. This Leetcode problem is done in many programming languages like C++, Java, and Python.

Two Sum Leetcode Solution
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.

Now, let’s see the leetcode solution of Two Sum Leetcode Solution.

 Two Sum Leetcode Solution in Python

This is an O(N) complexity solution.

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

 Two Sum Leetcode Solution in CPP

This is an O(N) complexity solution.

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

 Two Sum Leetcode Solution in Java

This is an O(N) complexity solution.

class Solution {
  public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> numToIndex = new HashMap<>();
    for (int i = 0; i < nums.length; ++i) {
      if (numToIndex.containsKey(target - nums[i]))
        return new int[] {numToIndex.get(target - nums[i]), i};
      numToIndex.put(nums[i], i);
    throw new IllegalArgumentException();

Note: This problem  Two Sum is generated by Leetcode but the solution is provided by Chase2learn This tutorial is only for Educational and Learning purposes.

Next: Add Two Numbers Leetcode Solution

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