217. Contains Duplicate

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

 

Constraints:

• 1 <= nums.length <= 105
• -109 <= nums[i] <= 109

Solution:

Rust

impl Solution {
    pub fn contains_duplicate(nums: Vec<i32>) -> bool {
        let mut set = std::collections::HashSet::new();

        for num in nums {
            if set.contains(num) {
                return true;
            } else {
                set.insert(num);
            }
        }
        false
    }
}

C#

public sealed class Solution
{
    /// <summary>
    /// Determines whether the given array contains any duplicate elements.
    /// </summary>
    /// <param name="numbers">The array to check for duplicates.</param>
    /// <returns>True if any element appears at least twice; otherwise, false.</returns>
    public bool ContainsDuplicate(int[] numbers)
    {
        var uniqueNumbers = new HashSet<int>(numbers.Length);

        foreach (var number in numbers)
        {
            if (!uniqueNumbers.Add(number)) return true;
        }

        return false;
    }

    /// alternative
    /// public bool ContainsDuplicate(int[] numbers) =>
    ///   numbers.Length > new HashSet<int>(numbers).Count;
}

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