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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.

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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

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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;
    }
}

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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;
    }
};

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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
}

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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;
}

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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;
    }
}

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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;
    }
}

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