> ## 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.

# Contains Duplicate II Python Solution

> Tested Python solution for LeetCode 219 with 15 pytest cases. Generate a practice environment with lcpy.

LeetCode 219, Easy. Topics: Array, Hash Table, Sliding Window. [View on LeetCode](https://leetcode.com/problems/contains-duplicate-ii/description/).

Generate this problem as a practice environment: tested reference solution, 15 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 219   # by problem number
lcpy gen -s contains_duplicate_ii   # by problem name
```

## Problem

Given an integer array `nums` and an integer `k`, return `true` \*if there are two **distinct indices** \* `i` *and* `j` *in the array such that* `nums[i] == nums[j]` *and* `abs(i - j) <= k`.

### Examples

```
Input: nums = [1,2,3,1], k = 3
Output: true
```

```
Input: nums = [1,0,1,1], k = 1
Output: true
```

```
Input: nums = [1,2,3,1,2,3], k = 2
Output: false
```

### Constraints

* 1 \<= nums.length \<= 10^5
* -10^9 \<= nums\[i] \<= 10^9
* 0 \<= k \<= 10^5

## Solution

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

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n)
    # Space: O(n)
    def contains_nearby_duplicate(self, nums: list[int], k: int) -> bool:
        last_seen: dict[int, int] = {}

        for i, num in enumerate(nums):
            if num in last_seen and i - last_seen[num] <= k:
                return True
            last_seen[num] = i

        return False
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(n) | O(n)  |

## Tags

[NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).