README.md

2310. Sum of Numbers With Units Digit K

Given two integers num and k, consider a set of positive integers with the following properties:

• The units digit of each integer is k.
• The sum of the integers is num.

Return the minimum possible size of such a set, or -1 if no such set exists.

Note:

• The set can contain multiple instances of the same integer, and the sum of an empty set is considered 0.
• The units digit of a number is the rightmost digit of the number.

Example 1:

Input: num = 58, k = 9
Output: 2
Explanation:
One valid set is [9,49], as the sum is 58 and each integer has a units digit of 9.
Another valid set is [19,39].
It can be shown that 2 is the minimum possible size of a valid set.

Example 2:

Input: num = 37, k = 2
Output: -1
Explanation: It is not possible to obtain a sum of 37 using only integers that have a units digit of 2.

Example 3:

Input: num = 0, k = 7
Output: 0
Explanation: The sum of an empty set is considered 0.

Constraints:

• 0 <= num <= 3000
• 0 <= k <= 9

Solutions (Rust)

1. Solution

impl Solution {
    pub fn minimum_numbers(num: i32, k: i32) -> i32 {
        if num == 0 {
            return 0;
        }

        let mut sum = k;

        for i in 1..=10 {
            if sum <= num && sum % 10 == num % 10 {
                return i;
            }
            sum += k;
        }

        -1
    }
}