Last updated on March 9th, 2025 at 10:33 pm

Here, we see a Contains Duplicate LeetCode Solution. This Leetcode problem is solved using different approaches in many programming languages, such as C++, Java, JavaScript, Python, etc.

List of all LeetCode Solution

Topics

Array, Hash Table

Companies

Airbnb, Palantir, Yahoo

Level of Question

Easy

Contains Duplicate LeetCode Solution

1. Problem Statement

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

Example 1:
Input: nums = [1,2,3,1]
Output: true

Example 2:
Input: nums = [1,2,3,4]
Output: false

Example 3:
Input: nums = [1,1,1,3,3,4,3,2,4,2]
Output: true

2. Coding Pattern Used in Solution

The coding pattern used here is “Hashing for Duplicate Detection”, which is not listed in the provided patterns. This pattern leverages hash-based data structures (like unordered_map, HashSet, Set) to efficiently check for duplicates.

3. Code Implementation in Different Languages

3.1 Contains Duplicate C++

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        if (nums.empty()) { return false; }
        unordered_map<int,int> mp;
        for (int i : nums) {
            if (++mp[i] > 1) {
                return true;
            }
        }
        return false;
    }
};

3.2 Contains Duplicate Java

class Solution {
    public boolean containsDuplicate(int[] nums) {
        if(nums==null || nums.length==0)
            return false;
        HashSet<Integer> hset = new HashSet<Integer>();
        for(int idx: nums){
            if(!hset.add(idx)){
                return true;
            }
        }
        return false;
    }
}

3.3 Contains Duplicate JavaScript

var containsDuplicate = function(nums) {
    const s = new Set(nums);
return s.size !== nums.length
};

3.4 Contains Duplicate Python

class Solution(object):
    def containsDuplicate(self, nums):
        return len(nums) != len(set(nums))

4. Time and Space Complexity

	Time Complexity	Space Complexity
C++	O(n)	O(n)
Java	O(n)	O(n)
JavaScript	O(n)	O(n)
Python	O(n)	O(n)