LeetCode | Regular Expression Matching

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

思路是分别处理a*、.*、.、a的情况。

三周前写的lengthy code如下：

 class Solution {
 public:
     bool isMatch(const char *s, const char *p) {
         int sn = strlen(s);
         int pn = strlen(p);
         return recursive(s, sn, p, pn);
     }

     bool recursive(const char* s, int sn, const char* p, int pn) {
         if (sn ==  && pn == ) return true;
         if (pn == ) return false;

         if (*(p + ) != '\0') {
             if (*(p + ) == '*') {
                 if (*p == '.') { // .*
                     int n = ;
                     while (n <= sn) {
                         if (recursive(s + n, sn - n, p + , pn - )) return true;
                         n++;
                     }
                 } else { // a*
                     int n = ;
                     while (n <= sn && *(s + n) == *p) {
                         if (recursive(s + n, sn - n, p + , pn - )) return true;
                         n++;
                     }
                     if (recursive(s + n, sn - n, p + , pn - )) return true;
                 }
             } else {
                 if (*p != '.' && *s != *p) return false;
                 if (recursive(s + , sn - , p + , pn - )) return true;
             }
         } else {
             if (*p != '.' && *s != *p) return false;
             if (recursive(s + , sn - , p + , pn - )) return true;
         }
     }
 };

今天看了Leetcode上1337的代码真是羞愧啊。http://leetcode.com/2011/09/regular-expression-matching.html

重写了一遍。思路还是一样。

 class Solution {
 public:
     bool isMatch(const char *s, const char *p) {
         if (*p == '\0') return (*s == '\0');
         // match single '\0', '.', 'a'...
         if (*(p + ) != '*') {
             return ((*s == *p || (*p == '.' && *s != '\0')) && isMatch(s + , p + ));
         }

         // match a*, .*
         while ((*s == *p || (*p == '.' && *s != '\0'))) {
             if (isMatch(s++, p + )) return true;
         }

         // ignore a*， *p != '.' && *s != *p
         return isMatch(s, p + );
     }
 };