Contains Duplicate II LeetCode Solution | Easy Approach

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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

Contains Duplicate II Solutions

Time: O(n)
Space: O(n)

C++

class Solution {
 public:
  bool containsNearbyDuplicate(vector<int>& nums, int k) {
    unordered_set<int> seen;

    for (int i = 0; i < nums.size(); ++i) {
      if (!seen.insert(nums[i]).second)
        return true;
      if (i >= k)
        seen.erase(nums[i - k]);
    }

    return false;
  }
};

Java

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

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

    return false;
  }
}

Python

 class Solution:
  def containsNearbyDuplicate(self, nums: List[int], k: int) -> bool:
    seen = set()

    for i, num in enumerate(nums):
      if i > k:
        seen.remove(nums[i - k - 1])
      if num in seen:
        return True
      seen.add(num)

    return False

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