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题目来源：https://leetcode.com/problems/regular-expression-matching/

Regular Expression Matching

‘.’匹配任意单个字符，‘*’匹配0个或多个前一字符。如果匹配整个串返回true。

例：

isMatch(“aa”,”a”) → false

isMatch(“aa”,”aa”) → true

isMatch(“aaa”,”aa”) → false

isMatch(“aa”, “a*”) → true

isMatch(“aa”, “.*”) → true

isMatch(“ab”, “.*”) → true

isMatch(“aab”, “c*a*b”) → true

解决方案转载自：/article/5002355.html

bool isMatch(const char *s, const char *p)
{
if (s == NULL || p == NULL) return false;
if (*p == '\0') return *s == '\0';
// ".*" matches "", so we can't check (*s == '\0') here.

if (*(p + 1) == '*')
{
// Here *p != '\0', so this condition equals with
// (*s != '\0' && (*p == '.' || *s == *p)).
while ((*s != '\0' && *p == '.') || *s == *p)
{
if (isMatch(s, p + 2)) return true;
++s;
}

return isMatch(s, p + 2);
}
else if ((*s != '\0' && *p == '.') || *s == *p)
{
return isMatch(s + 1, p + 1);
}

return false;
}