# Contains Duplicate II

## 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.

Example 1:

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

Example 2:

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

Example 3:

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

Constraints:

- 1 <= nums.length <= 105
- -109 <= nums[i] <= 109
- 0 <= k <= 105

## Solution

Time: O(n) Space: O(n)

```
class Solution {
public boolean containsNearbyDuplicate(int[] nums, int k) {
// key: number
// value: monotonic index
var m = new HashMap<Integer, Integer>();
for (var i = 0; i < nums.length; i++) {
var n = nums[i];
if (m.containsKey(n)) {
if (Math.abs(m.get(n) - i) <= k) {
return true;
}
}
m.put(n, i);
}
return false;
}
}
```