Package g1901_2000.s1922_count_good_numbers

Class Solution

java.lang.Object
g1901_2000.s1922_count_good_numbers.Solution
public class Solution extends java.lang.Object
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 109 + 7.

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:

  • 1 <= n <= 1015

  • Constructor Summary

    Constructors
    Constructor
    Description
    Solution()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    countGoodNumbers(long n)
     

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • countGoodNumbers

      public int countGoodNumbers(long n)