# 219. Contains Duplicate II

## 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 {
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;
}
};

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


• 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;
}
}

• 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;
}
}