Given an array of integers and an integer *k*, find out whether there are two distinct indices *i* and *j* in the array such that **nums[i] = nums[j]** and the **absolute** difference between *i* and *j* is at most *k*.

**Example 1:**

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

**Example 2:**

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

**Example 3:**

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

## Solution

public class Solution { public bool ContainsNearbyDuplicate(int[] nums, int k) { HashSet<int> set = new HashSet<int>(); for(int i=0;i<nums.Length;i++) { if(i > k) { set.Remove(nums[i-k-1]); } if(set.Contains(nums[i])) return true; else set.Add(nums[i]); } return false; } }

## Code Walk through

```
value = [ 1, 2, 3, 1]
index = [ 0, 1, 2, 3]
k = 3
i = 0;
set = { 1 }
i = 1;
set = { 1, 2}
i = 2;
set = { 1, 2, 3}
i = 3;
set = {1, 2, 3, 1} ----> Return True
```

```
value = [1,2,3,1,2,3]
index = [0,1,2,3,4,5]
k = 2
i = 0;
set = {1}
i = 1;
set = {1,2}
i = 2;
set = {1,2,3}
i = 3;
k = 2;
i > k -- So remove (i - k - 1) => 0th index element -- that is 1
so set will be - {2,3}
Now add the element as asusual in set
set = {2,3,1}
i = 4;
k = 2;
i > k -- So remove (i - k - 1) => 1st index element -- that is 2
so set will be - {3,1}
Now add the element as asusual in set
set = {3,1,2}
i = 5;
k = 2;
i > k -- So remove (i - k - 1) => 2nd index element -- that is 3
so set will be - {1,2}
Now add the element as asusual in set
set = {1,2,3}
-----> Return False
```

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