20 有效的括号

  1. class Solution {
  2.     public boolean isValid(String s) {
  3.         Stack<Character> buckets = new Stack<Character>();
  4.         buckets.push('#');  // 栈底压入标志
  5.         for (int i = 0; i < s.length(); i++) {
  6.             Character c = s.charAt(i);
  7.             switch (c) {
  8.                 case '(':
  9.                 case '[':
  10.                 case '{':
  11.                     buckets.push(c);
  12.                     break;
  13.                 case ')':
  14.                     if (buckets.peek() == '(')
  15.                         buckets.pop();
  16.                     else 
  17.                         return false;
  18.                     break;
  19.                 case ']':
  20.                     if (buckets.peek() == '[')
  21.                         buckets.pop();
  22.                     else
  23.                         return false;
  24.                     break;
  25.                 case '}':
  26.                     if (buckets.peek() == '{')
  27.                         buckets.pop();
  28.                     else
  29.                         return false;
  30.                     break;
  31.             }
  32.         }
  33.         if (buckets.peek() == '#')
  34.             return true;
  35.         else 
  36.             return false;
  37.     }
  38. }