LeetCode 10. Regular Expression Matching

Posted 2020-10-05 浩然

https://leetcode.com/problems/regular-expression-matching/description/

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

• 字符串匹配。最后一个样例中匹配是因为*可以是0次匹配，i.e. c0a2b。
• 递归法或者动态规划。

 1 //
 2 //  main.cpp
 3 //  LeetCode
 4 //
 5 //  Created by Hao on 2017/3/16.
 6 //  Copyright © 2017年 Hao. All rights reserved.
 7 //
 8 
 9 #include <iostream>
10 #include <string>
11 using namespace std;
12 
13 class Solution {
14 public:
15     bool isMatch(string s, string p) {
16         return isMatch(s.c_str(), p.c_str());
17     }
18 
19 private:
20     bool isMatch(const char *s, const char *p) {
21         if (*p == ‘\0‘) return *s == ‘\0‘;
22         
23         // next char is not ‘*‘, must match the current char
24         if (*(p + 1) != ‘*‘) {
25             if ((*p == *s) || ((*p == ‘.‘) && (*s != ‘\0‘)))
26                 return isMatch(s + 1, p + 1);
27             else
28                 return false;
29         } else { // next char is ‘*‘
30             // ‘*‘ matches zero or more of the preceding element
31             while ((*p == *s) || ((*p == ‘.‘) && (*s != ‘\0‘))) {
32                 // check if the remaining string matches
33                 if (isMatch(s, p + 2))
34                     return true;
35                 // move point
36                 s ++;
37             }
38             // next matching
39             return isMatch(s, p + 2);
40         }
41     }
42 };
43 
44 int main ()
45 {
46     Solution testSolution;
47     string sTest[] = {"aa", "a", "aa", "aa", "aaa", "aa", "aa", "a*", "aa", ".*", "ab", ".*", "aab", "c*a*b"};
48 
49     for (int i = 0; i < 7; i ++)
50         cout << testSolution.isMatch(sTest[2 * i], sTest[2 * i + 1]) << endl;
51     
52     return 0;
53 }

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