# 1397. Find All Good Strings

## Description

Given the strings `s1`

and `s2`

of size `n`

and the string `evil`

, return *the number of good strings*.

A **good** string has size `n`

, it is alphabetically greater than or equal to `s1`

, it is alphabetically smaller than or equal to `s2`

, and it does not contain the string `evil`

as a substring. Since the answer can be a huge number, return this **modulo** `10`

.^{9} + 7

**Example 1:**

Input:n = 2, s1 = "aa", s2 = "da", evil = "b"Output:51Explanation:There are 25 good strings starting with 'a': "aa","ac","ad",...,"az". Then there are 25 good strings starting with 'c': "ca","cc","cd",...,"cz" and finally there is one good string starting with 'd': "da".

**Example 2:**

Input:n = 8, s1 = "leetcode", s2 = "leetgoes", evil = "leet"Output:0Explanation:All strings greater than or equal to s1 and smaller than or equal to s2 start with the prefix "leet", therefore, there is not any good string.

**Example 3:**

Input:n = 2, s1 = "gx", s2 = "gz", evil = "x"Output:2

**Constraints:**

`s1.length == n`

`s2.length == n`

`s1 <= s2`

`1 <= n <= 500`

`1 <= evil.length <= 50`

- All strings consist of lowercase English letters.