Leetcode 219. Contains Duplicate II

Given an integer array nums and an integer k, return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= 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

Constraints:

• 1 <= nums.length <= 105
• -109 <= nums[i] <= 109
• 0 <= k <= 105

We can use a dictionary to remember the lastest appeared number and it’s index. The condition wants abs(i – j) <= k, so it means, the closer the distance between ‘i’ and ‘j,’ the better. That’s why we only need to cache the lastest appeared number and it’s index.

class Solution:
    def containsNearbyDuplicate(self, nums: List[int], k: int) -> bool:
        check_dict = {}

        for index, num in enumerate(nums):
            if num in check_dict and abs(check_dict[num] - index) <= k:
                return True
            check_dict[num] = index
        return False