219_ContainsDuplicateII.java

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

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