Create 0219-contains-duplicate-II.cs

Author: vermavarun

csharp/0219-contains-duplicate-II.cs

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+/*
+
+Approach:
+1. We will use a HashSet to store the elements.
+2. We will iterate through the array and add the elements to the HashSet.
+3. If the element is already present in the HashSet, we will return true.
+4. If the difference between the current index and the previous index is greater than k, we will remove the element at the previous index.
+5. If we reach the end of the array, we will return false.
+
+Time Complexity: O(n)
+Space Complexity: O(n)
+
+*/
+public class Solution {
+    public bool ContainsNearbyDuplicate(int[] nums, int k) {
+        HashSet<int> hs = new HashSet<int>();
+        int i,j;
+        i = j = 0;
+        while(j<nums.Length) {
+            if( Math.Abs(i-j) <= k) {
+                if(!hs.Contains(nums[j])) {
+                    hs.Add(nums[j]);
+                    j++;
+                }
+                else {
+                    return true;
+                }
+            }
+            else {
+                hs.Remove(nums[i]);
+                i++;
+            }
+        }
+        return false;
+    }
+}