Question

219. Contains Duplicate II

中文文档

Description

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

Solutions

Solution 1: Hash Table

We use a hash table $d$ to store the nearest index of the number it has visited.

We traverse the array nums. For the current element $nums[i]$, if it exists in the hash table, and the difference between its index and the current index is no larger than $k$, then return true. Otherwise, we add the current element into the hash table.

After the traversal, return false.

The time complexity is $O(n)$ and the space complexity is $O(n)$. Here $n$ is the length of array nums.

class Solution:
  def containsNearbyDuplicate(self, nums: List[int], k: int) -> bool:
    d = {}
    for i, x in enumerate(nums):
      if x in d and i - d[x] <= k:
        return True
      d[x] = i
    return False

class Solution {
  public boolean containsNearbyDuplicate(int[] nums, int k) {
    Map<Integer, Integer> d = new HashMap<>();
    for (int i = 0; i < nums.length; ++i) {
      if (i - d.getOrDefault(nums[i], -1000000) <= k) {
        return true;
      }
      d.put(nums[i], i);
    }
    return false;
  }
}

class Solution {
public:
  bool containsNearbyDuplicate(vector<int>& nums, int k) {
    unordered_map<int, int> d;
    for (int i = 0; i < nums.size(); ++i) {
      if (d.count(nums[i]) && i - d[nums[i]] <= k) {
        return true;
      }
      d[nums[i]] = i;
    }
    return false;
  }
};

func containsNearbyDuplicate(nums []int, k int) bool {
  d := map[int]int{}
  for i, x := range nums {
    if j, ok := d[x]; ok && i-j <= k {
      return true
    }
    d[x] = i
  }
  return false
}

function containsNearbyDuplicate(nums: number[], k: number): boolean {
  const d: Map<number, number> = new Map();
  for (let i = 0; i < nums.length; ++i) {
    if (d.has(nums[i]) && i - d.get(nums[i])! <= k) {
      return true;
    }
    d.set(nums[i], i);
  }
  return false;
}

public class Solution {
  public bool ContainsNearbyDuplicate(int[] nums, int k) {
    var d = new Dictionary<int, int>();
    for (int i = 0; i < nums.Length; ++i) {
      if (d.ContainsKey(nums[i]) && i - d[nums[i]] <= k) {
        return true;
      }
      d[nums[i]] = i;
    }
    return false;
  }
}

class Solution {
  /**
   * @param Integer[] $nums
   * @param Integer $k
   * @return Boolean
   */
  function containsNearbyDuplicate($nums, $k) {
    $hashtable = [];
    for ($i = 0; $i < count($nums); $i++) {
      $tmp = $nums[$i];
      if (array_key_exists($tmp, $hashtable) && $k >= $i - $hashtable[$tmp]) {
        return true;
      }
      $hashtable[$tmp] = $i;
    }
    return false;
  }
}