Contains Duplicate

217. Contains Duplicate​

Description:
You are given an array of integers, nums, which may contain both positive and negative numbers. Your task is to determine whether any value appears more than once in the array. If at least one duplicate exists, return true. Otherwise, return false.

Video Explanation​

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Example 1:​

Input:
nums = [1, 2, 3, 1]

Output:
true (because 1 appears twice)

Explanation:

• The frequency of 1 is 2
• The frequency of 2 is 1
• The frequency of 3 is 1
• Since 1 appears twice, there is a duplicate, so the output is true.

Example 2:​

Input:
nums = [1, 2, 3, 4]

Output:
false (because all elements are distinct)

Explanation:

• All elements are unique and appear only once.

Solutions​

#include <iostream>
#include <unordered_set>
#include <vector>

using namespace std;

bool containsDuplicate(const vector<int>& nums) {
    unordered_set<int> uniques;
    
    for (int num : nums) {
        // If the number is already in the set, it means it's a duplicate
        if (uniques.find(num) != uniques.end()) {
            return true;
        }
        // Add the number to the set
        uniques.insert(num);
    }
    return false;
}

int main() {
    vector<int> nums = {1, 2, 3, 1}; // Example input
    if (containsDuplicate(nums)) {
        cout << "Array contains duplicates." << endl;
    } else {
        cout << "Array does not contain duplicates." << endl;
    }
    
    return 0;
}

import java.util.HashSet;
import java.util.Set;

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Set<Integer> set = new HashSet<>();
        for (int num : nums) {
            if (!set.add(num)) {
                return true;
            }
        }
        return false;
    }
}

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        return len(nums) != len(set(nums))

var containsDuplicate = function(nums) {
    const set = new Set();
    for (const num of nums) {
        if (set.has(num)) return true;
        set.add(num);
    }
    return false;
};