2413 - Smallest Even Multiple (Easy)

Problem Link

https://leetcode.com/problems/smallest-even-multiple/

Problem Statement

Given a positive integer n, return the smallest positive integer that is a multiple of both 2 and n.

Example 1:

Input: n = 5
Output: 10
Explanation: The smallest multiple of both 5 and 2 is 10.

Example 2:

Input: n = 6
Output: 6
Explanation: The smallest multiple of both 6 and 2 is 6. Note that a number is a multiple of itself.

Constraints:

• 1 <= n <= 150

Approach 1: n or 2n

The smallest multiple of 2 and a number $n$ will be either

• $n$ if $n$ is even
• $2n$ if $n$ is odd

In solution we need to first check if the number is even and return the correct result.

Java

Written by @kat-kan

class Solution {
    public int smallestEvenMultiple(int n) {
        if (n % 2 == 0) return n;
        return n * 2;
    }
}

Time complexity :

$O(1)$ : It takes a constant time. There is one input variable and the algorithm will take the same time no matter of value.

Space complexity :

$O(1)$ : There is one int variable (4 bytes of memory) and algorithm will always take 4 bytes of memory to complete. The space complexity is constant.

Approach 2: Ternary operator

We can make our solution much shorter using ternary operator:

• $n \% 2$ is a condition
• $n$ is returned when condition is true
• $n * 2$ is returned when condition is false

Java

Written by @kat-kan

class Solution {
    public static int smallestEvenMultiple(int n) {
        return n % 2 == 0 ? n : n * 2;
    }
}

Time Complexity

$O(1)$ : It takes a constant time. There is one input variable and the algorithm will take the same time no matter of value.

Space Complexity

$O(1)$ : There is one int variable (4 bytes of memory) and algorithm will always take 4 bytes of memory to complete. The space complexity is constant.