[leetcode] 301. Remove Invalid Parentheses

Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results.

Note: The input string may contain letters other than the parentheses ( and ).

Examples:

"()())()" -> ["()()()", "(())()"]
"(a)())()" -> ["(a)()()", "(a())()"]
")(" -> [""] 

Credits:
Special thanks to @hpplayer for adding this problem and creating all test cases.

Solution:

BFS, 使用validParenthese判断是否合法括号。如果不是合法，则依次去掉第i个括号继续判断。

 1 vector<string> removeInvalidParentheses(string s)
 2     {
 3         vector<string> ret;
 4         unordered_set<string> visit;
 5         queue<string> Q;
 6         Q.push(s);
 7         visit.insert(s);
 8
 9         bool found = false;
10         while (!Q.empty())
11         {
12             string ts = Q.front();
13             Q.pop();
14             if (validParenthese(ts)) // valid parenthese, continue
15             {
16                 ret.push_back(ts);
17                 found = true;
18             }
19             if (found == true)
20                 continue;
21
22             for (int i = 0; i < ts.size(); i++)
23             {
24                 if ((ts[i] != ‘(‘) && (ts[i] != ‘)‘))
25                     continue;
26                 string temp = ts.substr(0, i) + ts.substr(i + 1);
27                 if (visit.find(temp) == visit.end())
28                 {
29                     visit.insert(temp);
30                     Q.push(temp);
31                 }
32             }
33         }
34
35         return ret;
36     }
37
38     bool validParenthese(string s)
39     {
40         int mleft = 0;
41         for (int i = 0; i < s.size(); i++)
42         {
43             if (s[i] == ‘(‘)
44                 mleft++;
45             if (s[i] == ‘)‘)
46                 mleft--;
47             if (mleft < 0)
48                 return false;
49         }
50
51         return (mleft == 0);
52     }