> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# 3Sum Closest Python Solution with Tests

> Tested Python solution for LeetCode 16 with 16 pytest cases. Generate a practice environment with lcpy.

LeetCode 16, Medium. Topics: Array, Two Pointers, Sorting. [View on LeetCode](https://leetcode.com/problems/three-sum-closest/description/).

Generate this problem as a practice environment: tested reference solution, 16 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 16   # by problem number
lcpy gen -s three_sum_closest   # by problem name
```

## Problem

Given an integer array `nums` of length `n` and an integer `target`, find three integers at **distinct indices** in `nums` such that the sum is closest to `target`.

Return *the sum of the three integers*.

You may assume that each input would have exactly one solution.

### Examples

```
Input: nums = [-1,2,1,-4], target = 1
Output: 2
Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).
```

```
Input: nums = [0,0,0], target = 1
Output: 0
Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0).
```

### Constraints

* 3 \<= nums.length \<= 500
* -1000 \<= nums\[i] \<= 1000
* -10^4 \<= target \<= 10^4

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/three_sum_closest/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/three_sum_closest/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n^2)
    # Space: O(1) (ignoring sort space)
    def three_sum_closest(self, nums: list[int], target: int) -> int:
        nums.sort()
        n = len(nums)
        closest = nums[0] + nums[1] + nums[2]

        for i in range(n - 2):
            left = i + 1
            right = n - 1
            while left < right:
                current_sum = nums[i] + nums[left] + nums[right]
                # Update closest if this sum is nearer to target
                if abs(current_sum - target) < abs(closest - target):
                    closest = current_sum
                if current_sum == target:
                    return current_sum
                elif current_sum < target:
                    left += 1
                else:
                    right -= 1

        return closest
```

## Complexity

| Time   | Space                      |
| ------ | -------------------------- |
| O(n^2) | O(1) (ignoring sort space) |

## Tags

[Grind](/catalog/grind).