g1901_2000.s1922_count_good_numbers

Class Solution

java.lang.Object

g1901_2000.s1922_count_good_numbers.Solution

public class Solution
extends 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 and Description
Solution()

Method Summary

Modifier and Type	Method and Description
int	countGoodNumbers(long n)

Methods inherited from class java.lang.Object

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

Constructor Detail

Solution

public Solution()

Method Detail

countGoodNumbers

public int countGoodNumbers(long n)