Regular Expression Matching

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

思想：如果*(p+1) == '*'， 则p可能匹配也可能不匹配；

C++代码：

// char '\0' or 0 a=2,b=a++; b=2;a=3

1. bool isMatch(const char *s, const char *p) {
2. if( *p == 0) return *s == 0;
3. const char *q;
4. // q=p++;
5. if(*(p+1) != '*') {
6. if(*s == *p || (*p == '.' && (*s) != 0)) return isMatch(s+1,p+1);
7. else return false;
8. } else {
9. while(*s == *p || (*p == '.' && (*s) != 0)) {
10. if(isMatch(s,p+2)) {
11. return true;
12. }
13. s++;
14. }
15. return isMatch(s,p+2);
16. }
17. }

java代码：

1. public boolean isMatch(String s, String p) {
2. int s1 = s.length();
3. int p1 = p.length();
4. if(p1==0) return s1==0;
5. if(p1==1) return s1==1 && (s.charAt(0)==p.charAt(0) || p.charAt(0)=='.');
6. //if(p1==1 && s1>1) return false;
7. int i=0;
8. int j=0;
9. if(p.charAt(j+1) != '*') {
10. if(i<s1 && (p.charAt(j) == s.charAt(i) || (p.charAt(j)=='.'))) {
11. return isMatch(s.substring(i+1),p.substring(j+1));
12. }
13. else return false;
14. }else {
15. while(i<s1 && (p.charAt(j) == s.charAt(i) || (p.charAt(j)=='.'))) {
16. if(isMatch(s.substring(i),p.substring(j+2))) {
17. return true;
18. }
19. i++;
20. }
21. return isMatch(s.substring(i),p.substring(j+2));
22. }
23. // return false;
24. }