FB面经 Prepare: Make Parentheses valid

给一组括号，remove最少的括号使得它valid

从左从右各scan一次

 1 package fb;
 2 
 3 public class removeParen {
 4     
 5     public static String fix(String str) {
 6         StringBuffer res = new StringBuffer(str);
 7         int l = 0, r = 0;
 8         int i = 0;
 9         while (i < res.length()) {
10             if (res.charAt(i) == '(') l++;
11             else {
12                 if (l <= r) {
13                     res.deleteCharAt(i);
14                     i--;
15                 }
16                 else {
17                     r++;
18                 }
19             }
20             i++;
21         }
22         
23         l = 0;
24         r = 0;
25         i = res.length()-1;
26         while (i >= 0) {
27             if (res.charAt(i) == ')') r++;
28             else {
29                 if (l >= r) {
30                     res.deleteCharAt(i);
31                 }
32                 else {
33                     l++;
34                 }
35             }
36             i--;
37         }
38         
39         return res.toString();
40     }
41     
42 
43     /**
44      * @param args
45      */
46     public static void main(String[] args) {
47         // TODO Auto-generated method stub
48         String res = fix(")((())(");
49         System.out.println(res);
50     }
51 
52 }