Sum of numbers with units digit k

Math Dynamic Programming Greedy Enumeration

28.1% acceptance

Feb 25, 2026

428

338

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.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn minimum_numbers(num: i32, k: i32) -> i32 {
    if num == 0 {
      return 0;
    }
    if k == 0 {
      return if num % 10 == 0 { 1 } else { -1 };
    }
    for count in 1..=10i32 {
      if (k * count) % 10 == num % 10 && k * count <= num {
        return count;
      }
    }
    -1
  }
}