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

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;
}