Contains Duplicate II LT219

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

Example 1:

Input: nums = [1,2,3,1], k = 3
Output: true

Example 2:

Input: nums = [1,0,1,1], k = 1
Output: true

Example 3:

Input: nums = [1,2,3,1,2,3], k = 2
Output: false

Idea 1. Sliding window + HashMap(Set), note there are k+1 values in the window for [0, k].

Time complexity: O(N)

Space complexity: O(k+1)

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

Idea 1.b HashMap with index, pair (nums[i], i), 

Time complexity: O(N)

Space complexity: O(N)

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