ContainsDuplicateII.java

import java.util.HashMap;
import java.util.HashSet;

/**
 * https://leetcode.com/articles/contains-duplicate-ii/
 */
public class ContainsDuplicateII {

    public boolean containsNearbyDuplicate(int[] nums, int k) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            Integer idx = map.get(nums[i]);
            if (idx != null && i - idx <= k) {
                return true;
            }
            map.put(nums[i], i);
        }
        return false;
    }

    public boolean containsNearbyDuplicate2(int[] nums, int k) {
        HashSet<Integer> set = new HashSet<>();
        for (int i = 0; i < nums.length; i++) {
            if (i >= k + 1) {
                set.remove(nums[i - k - 1]);
            }
            if (!set.add(nums[i])) {
                return true;
            }
        }
        return false;
    }
}