1     public static boolean isValid(String str) { 2         if (str == null) { 3             throw new IllegalArgumentException("Input error"); 4         } 5         // 0长度特殊处理 6         if (str.length() == 0) { 7             return true; 8         } 9         // 长度为奇数可以直接判断false10         if (str.length() % 2 == 1) {11             return false;12         }13         char[] array = str.toCharArray();14         // 维护左括号的集合15         List
     
       leftList = new ArrayList<>();16         for (int i = 0; i < array.length; i++) {17             if (getDirection(array[i]) == 1) {18                 // 左括号处理19                 leftList.add(array[i]);20             } else if (getDirection(array[i]) == -1) {21                 // 右括号处理22                 if (leftList.size() == 0) {23                     return false;24                 } else {25                     // 题目认为"({})"也是合理的形式26                     Character last = leftList.get(leftList.size() - 1);27                     if (getDirection(last) == -getDirection(array[i]) && getLevel(last) == getLevel(array[i])) {28                         leftList.remove(leftList.size() - 1);29                     } else {30                         return false;31                     }32                 }33             } else {34                 throw new IllegalArgumentException("Input error");35             }36         }37         // 循环结束之后判断leftList是否还有剩余38         if (leftList.size() != 0) {39             return false;40         }41         return true;42     }43 44     // 括号级别45     private static int getLevel(Character c) {46         switch (c) {47         case '{':48         case '}':49             return 3;50         case '[':51         case ']':52             return 2;53         case '(':54         case ')':55             return 1;56         default:57             return 0;58         }59     }60 61     // 括号方向62     private static int getDirection(Character c) {63         switch (c) {64         case '{':65         case '[':66         case '(':67             return 1;68         case '}':69         case ']':70         case ')':71             return -1;72         default:73             return 0;74         }75     }