Regular Expression Matching

正則比對

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      

1 package com.rust.TestString;
 2 
 3 class Solution {
 4     public boolean isMatch(String s, String p) {
 5         if (p.length() == 0) {
 6             return s.length() == 0;
 7         }
 8         if (p.length() == 1) {
 9             return (s.length() == 1) && (p.charAt(0) == s.charAt(0) || p.charAt(0) == '.');
10         }
11         // next char is not '*': must match current character
12         if (p.charAt(1) != '*') {
13             if (s.length() == 0) {
14                 return false;
15             } else {
16                 return (s.charAt(0) == p.charAt(0) || p.charAt(0) == '.')
17                         && isMatch(s.substring(1), p.substring(1));  // judge next char
18             }
19         } else {    // next char is '*'
20             while (s.length() > 0 && (p.charAt(0) == s.charAt(0) || p.charAt(0) == '.')) {
21                 if (isMatch(s, p.substring(2))) {
22                     return true;
23                 }
24                 s = s.substring(1);
25             }
26             return isMatch(s, p.substring(2));
27         }
28     }
29 }
30 
31 
32 public class RegularExpressionMatching {
33     public static void main(String args[]){
34         Solution solution = new Solution();
35         String s = "abcdefg";
36         System.out.println(solution.isMatch(s, "abcde*"));
37         System.out.println(solution.isMatch(s, ".*"));
38         System.out.println(solution.isMatch("abcdefg", "a.*"));
39         System.out.println(solution.isMatch("abcdefg", ".b."));
40         System.out.println(solution.isMatch("abcdefg", ""));
41         System.out.println(s);
42     }
43 }      

輸出：

false

true

abcdefg