Package g1901_2000.s1922_count_good_numbers

Class Solution

  • All Implemented Interfaces:
    
public final class Solution

    1922 - Count Good Numbers.

    Medium

    A digit string is good if the digits (0-indexed) at even indices are even and the digits at odd indices are prime (2, 3, 5, or 7).

    • For example, "2582" is good because the digits (2 and 8) at even positions are even and the digits (5 and 2) at odd positions are prime. However, "3245" is not good because 3 is at an even index but is not even.

    Given an integer n, return the total number of good digit strings of length n. Since the answer may be large, return it modulo <code>10<sup>9</sup> + 7</code>.

    A digit string is a string consisting of digits 0 through 9 that may contain leading zeros.

    Example 1:

    Input: n = 1

    Output: 5

    Explanation: The good numbers of length 1 are "0", "2", "4", "6", "8".

    Example 2:

    Input: n = 4

    Output: 400

    Example 3:

    Input: n = 50

    Output: 564908303

    Constraints:

    • <code>1 <= n <= 10<sup>15</sup></code>

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description

    • Field Summary

      Fields 
      Modifier and Type Field Description

    • Constructor Summary

      Constructors 
      Constructor Description
      Solution()

    • Enum Constant Summary

      Enum Constants 
      Enum Constant Description

    • Method Summary

      Modifier and Type Method Description
      final Integer countGoodNumbers(Long n)

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait