#2310
Sum of Numbers With Units Digit K
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math · dynamic programming · greedy · enumeration
Description
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.
Solution