ContainsDuplicate2.java

package array;

import java.util.HashSet;
import java.util.Set;

/**
 * Description: https://leetcode.com/problems/contains-duplicate-ii
 * Difficulty: Easy
 * Time complexity: O(n)
 * Space complexity: O(k)
 */
public class ContainsDuplicate2 {

    public boolean containsNearbyDuplicate(int[] nums, int k) {
        Set<Integer> seen = new HashSet<>();

        for (int i = 0; i < nums.length; i++) {
            if (i > k) seen.remove(nums[i - k - 1]);
            if (!seen.add(nums[i])) return true;
        }

        return false;
    }
}