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

 package fb;
 
 public class removeParen {
 
     public static String fix(String str) {
         StringBuffer res = new StringBuffer(str);
         int l = 0, r = 0;
         int i = 0;
         while (i < res.length()) {
             if (res.charAt(i) == '(') l++;
             else {
                 if (l <= r) {
                     res.deleteCharAt(i);
                     i--;
                 }
                 else {
                     r++;
                 }
             }
             i++;
         }
 
         l = 0;
         r = 0;
         i = res.length()-1;
         while (i >= 0) {
             if (res.charAt(i) == ')') r++;
             else {
                 if (l >= r) {
                     res.deleteCharAt(i);
                 }
                 else {
                     l++;
                 }
             }
             i--;
         }
 
         return res.toString();
     }
 
     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         String res = fix(")((())(");
         System.out.println(res);
     }
 
 }