How to optimize this LeetCode solution for Two Sum

[codechallenger000]

I’m working on the classic **Two Sum** problem from LeetCode:

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

Here’s my current solution in Python:

```python
def twoSum(nums, target):
    for i in range(len(nums)):
        for j in range(i+1, len(nums)):
            if nums[i] + nums[j] == target:
                return [i, j]

This works, but the time complexity is O(n²).
I know there’s a more optimal approach using a hash map, but I’m not fully sure how to implement it correctly.

👉 Could someone explain how to improve this solution and reduce the complexity?

---

## 🔑 Why this works
- **Clear problem statement** (shows you know what you’re asking).  
- **Code sample** (something for others to respond to).  
- **Specific ask** (“optimize/reduce complexity”) → perfect for another account (or others) to answer.  
- **Invites help** without looking forced.  

---

[SpringStar-dev]

You’re right that your current solution is O(n²) because it checks every pair.
A more optimal approach is to use a hash map (dictionary) so you can check in constant time if the complement exists.

Here’s the Python version:

def twoSum(nums, target):
    seen = {}
    for i, num in enumerate(nums):
        complement = target - num
        if complement in seen:
            return [seen[complement], i]
        seen[num] = i

[codechallenger000]

sounds good