Implement regular expression matching with support for '.' and '*'.
'.' Matches any single character.
'*' Matches zero or more of the preceding element.
The matching should cover the entire input string (not partial).
The function prototype should be:
bool isMatch(const char *s, const char *p)
Some examples:
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
思考：难度4.9，参考这里。
bool isMatch(const char *s, const char *p)
{
assert(s && p);
if (*p == ' ') return *s == ' ';
// next char is not '*': must match current character
if (*(p+1) != '*')
{
assert(*p != '*');
return ((*p == *s) || (*p == '.' && *s != ' ')) && isMatch(s+1, p+1); }
// next char is '*'
while ((*p == *s) || (*p == '.' && *s != ' '))
{
if (isMatch(s, p+2)) return true;
s++;
}
return isMatch(s, p+2);
}