find-all-good-strings

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Algorithms

Given the strings <code>s1</code> and <code>s2</code> of size <code>n</code> and the string <code>evil</code>, return the number of good strings.

A good string has size <code>n</code>, it is alphabetically greater than or equal to <code>s1</code>, it is alphabetically smaller than or equal to <code>s2</code>, and it does not contain the string <code>evil</code> as a substring. Since the answer can be a huge number, return this modulo <code>109 + 7</code>.

&nbsp;
Example 1:

<pre>
Input: n = 2, s1 = &quot;aa&quot;, s2 = &quot;da&quot;, evil = &quot;b&quot;
Output: 51 
Explanation: There are 25 good strings starting with &#39;a&#39;: &quot;aa&quot;,&quot;ac&quot;,&quot;ad&quot;,...,&quot;az&quot;. Then there are 25 good strings starting with &#39;c&#39;: &quot;ca&quot;,&quot;cc&quot;,&quot;cd&quot;,...,&quot;cz&quot; and finally there is one good string starting with &#39;d&#39;: &quot;da&quot;.&nbsp;
</pre>

Example 2:

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

Example 3:

<pre>
Input: n = 2, s1 = &quot;gx&quot;, s2 = &quot;gz&quot;, evil = &quot;x&quot;
Output: 2
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>s1.length == n</code></li>
	<li><code>s2.length == n</code></li>
	<li><code>s1 &lt;= s2</code></li>
	<li><code>1 &lt;= n &lt;= 500</code></li>
	<li><code>1 &lt;= evil.length &lt;= 50</code></li>
	<li>All strings consist of lowercase English letters.</li>
</ul>

findGoodStrings

Find All Good Strings

String

Dynamic Programming

String Matching

给你两个长度为 <code>n</code>&nbsp;的字符串&nbsp;<code>s1</code> 和&nbsp;<code>s2</code>&nbsp;，以及一个字符串&nbsp;<code>evil</code>&nbsp;。请你返回 好字符串&nbsp;的数目。

好字符串&nbsp;的定义为：它的长度为&nbsp;<code>n</code>&nbsp;，字典序大于等于&nbsp;<code>s1</code>&nbsp;，字典序小于等于&nbsp;<code>s2</code>&nbsp;，且不包含&nbsp;<code>evil</code>&nbsp;为子字符串。

由于答案可能很大，请你返回答案对 10^9 + 7 取余的结果。

&nbsp;

示例 1：

<pre>输入：n = 2, s1 = &quot;aa&quot;, s2 = &quot;da&quot;, evil = &quot;b&quot;
输出：51 
解释：总共有 25 个以 &#39;a&#39; 开头的好字符串：&quot;aa&quot;，&quot;ac&quot;，&quot;ad&quot;，...，&quot;az&quot;。还有 25 个以 &#39;c&#39; 开头的好字符串：&quot;ca&quot;，&quot;cc&quot;，&quot;cd&quot;，...，&quot;cz&quot;。最后，还有一个以 &#39;d&#39; 开头的好字符串：&quot;da&quot;。
</pre>

示例 2：

<pre>输入：n = 8, s1 = &quot;leetcode&quot;, s2 = &quot;leetgoes&quot;, evil = &quot;leet&quot;
输出：0 
解释：所有字典序大于等于 s1 且小于等于 s2 的字符串都以 evil 字符串 &quot;leet&quot; 开头。所以没有好字符串。
</pre>

示例 3：

<pre>输入：n = 2, s1 = &quot;gx&quot;, s2 = &quot;gz&quot;, evil = &quot;x&quot;
输出：2
</pre>

&nbsp;

提示：

<ul>
	<li><code>s1.length == n</code></li>
	<li><code>s2.length == n</code></li>
	<li><code>s1 &lt;= s2</code></li>
	<li><code>1 &lt;= n &lt;= 500</code></li>
	<li><code>1 &lt;= evil.length &lt;= 50</code></li>
	<li>所有字符串都只包含小写英文字母。</li>
</ul>