219. Contains Duplicate II

package Leetcode.SlideWindow;

import java.util.HashSet;

/**
 * @author zhengxingxing
 * @date 2025/01/29
 */
public class ContainsDuplicateII {

  public static boolean containsNearbyDuplicate(int[] nums, int k) {
    // Using HashSet as a sliding window to store elements
    HashSet<Integer> set = new HashSet<>();

    // Iterate through the array
    for (int i = 0; i < nums.length; i++) {
      // If window size exceeds k, remove the leftmost element
      // This maintains the window size of k elements
      if (i > k) {
        set.remove(nums[i - k - 1]);
      }

      // Try to add current element to set
      // If addition fails, it means element already exists in window
      // Therefore, we found duplicates within distance k
      if (!set.add(nums[i])) {
        return true;
      }
    }
    // No duplicates found within distance k
    return false;
  }

  public static void main(String[] args) {
    // Test Case 1: Should return true
    // Contains duplicate 1's with distance 3
    int[] nums1 = {1, 2, 3, 1};
    int k1 = 3;
    System.out.println("Test Case 1 Result: " + containsNearbyDuplicate(nums1, k1));

    // Test Case 2: Should return true
    // Contains duplicate 1's with distance 1
    int[] nums2 = {1, 0, 1, 1};
    int k2 = 1;
    System.out.println("Test Case 2 Result: " + containsNearbyDuplicate(nums2, k2));

    // Test Case 3: Should return false
    // No duplicates within distance 2
    int[] nums3 = {1, 2, 3, 1, 2, 3};
    int k3 = 2;
    System.out.println("Test Case 3 Result: " + containsNearbyDuplicate(nums3, k3));
  }
}