hihoCoder #1110 Regular Expression

 1 #include <iostream>
 2 #include <cstring>
 3 #include <string>
 4 #include <stack>
 5 std::string str;
 6 
 7 int find(std::string s)
 8 {
 9     std::stack<int> _SIndex;
10     int i = 0;
11     while (i < s.length()) {
12         if (s[i] == ‘(‘) {
13             _SIndex.push(i);
14         }
15         else if (s[i] == ‘)‘) {
16             if (_SIndex.empty())
17                 return -1;
18             else {
19                 _SIndex.pop();
20             }
21         }
22         ++i;
23     }
24 
25     if (_SIndex.size() == 1 ) {
26         return _SIndex.top();
27     }
28     else return -1;
29 }
30 
31 int regular(int s, int e) 
32 {
33     if (e < s) return 0;
34     if (s == e) return (str[s] == ‘0‘ || str[e] == ‘1‘);
35     if (str[e] == ‘*‘) {
36         return regular(s, e-1);
37     }
38     else if (str[e] == ‘)‘) {
39         std::string sub = str.substr(s, e-s);
40         int pos  = find(sub);
41         if (pos == -1) return 0;
42         else {
43             if (pos > 0) {
44                 if (str[s+pos-1] == ‘|‘) {
45                     return regular(s, s+pos-2) && regular(s+pos+1, e-1);
46                 }
47                 return  regular(s, s+pos-1) && regular(s+pos+1, e-1);
48             }
49             else return regular(s+1, e-1);
50         }
51     }
52     else {
53         if (str[e] == ‘0‘ || str[e] == ‘1‘) {
54             if (str[e-1] == ‘|‘) return regular(s, e-2);
55             else return regular(s, e-1);
56         }
57         else return 0;
58     }
59 }
60 
61 
62 int main()
63 {
64     while (1) {
65         std::getline(std::cin, str);
66         if (str.length()) {
67             if (regular( 0, str.length()-1)) {
68                 std::cout << "yes" << std::endl;
69             }
70             else std::cout << "no" << std::endl;
71         }
72         else break;
73     }
74 }