括号匹配检测

表达式有多种括号，包括[ ]、( )、{ }。本程序将检测用户输入的表达式是否合法，合法就输出YES，非法输出NO。

 

主要知识点:栈

 

㊣ StackX

 

/**

 * 栈实现

 * @author bbflyerwww

 * @date 2006-08-10

 */

 

public class StackX {

   

    private int maxSize;

   

    private char[] stack;

   

    private int top;

   

    public StackX() {

       maxSize = 1000;

       stack = new char[maxSize];

       top = -1;

    }

   

    public void push(char c) {

       top++;

       if (top >= maxSize)

           System.out.println("StackX is full...");

       else

           stack[top] = c;

    }

   

    public char pop() {

       char c;

       if (top < 0) {

           System.out.println("StackX is empty...");

           c = 0;

       } else

           c = stack[top--];

       return c;

    }

   

    public char peek() {

       char c;

       if (top < 0) {

           System.out.println("StackX is empty...");

           c = 0;

       } else

           c = stack[top];

       return c;

    }

   

    public boolean isEmpty() {

       return top == -1;

    }

   

    public boolean isFull() {

       return top == maxSize-1;

    }

 

}

 

㊣ BacketChecker

 

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

 

/**

 * 括号匹配

 * @author bbflyerwww

 * @date 2006-08-10

 */

 

public class BacketChecker {

   

    public static boolean check(String str) {

       StackX sx = new StackX();

       boolean flag = true;

       int k = str.length();

       for (int i = 0; i < k && flag; i++) {

           char c = str.charAt(i);

           if (c == '(' || c == '[' || c == '{')

              sx.push(c);

           else if (c == ')' || c == ']' || c == '}') {

              char x = sx.pop();

              switch (c) {

                  case ')':

                      if (x != '(') flag = false;

                      break;

                  case ']':

                      if (x != '[') flag = false;

                       break;

                  case '}':

                      if (x != '{') flag = false;

                      break;

                  default:

                      break;

              }

           } else {

              ;

           }

       }

       if (!sx.isEmpty())

           flag = false;

       return  flag;

    }

 

    public static void main(String[] args) throws IOException {

       BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

       String line = "";

       System.out.println("/t/tBacket Matcher/t/t" +

              "/n/t1 Input string like a[b(c)de]f{g}" +

              "/n/t2 Q to Exit");

       while (true) {

           System.out.print("/tInput : ");

           line = br.readLine();

           if (line.equals("Q") || line.equals("q"))

              break;

           System.out.print("/tResult : ");         

           if (check(line))

              System.out.println("YES");

           else

              System.out.println("NO");

       }

    }

 

}

 

㊣ 说明: java.util.Stack<E>类

 

   The Stack class represents a last-in-first-out (LIFO) stack of objects. It extends class Vector with five operations that allow a vector to be treated as a stack. The usual push and pop operations are provided, as well as a method to peek at the top item on the stack, a method to test for whether the stack is empty, and a method to search the stack for an item and discover how far it is from the top.

   When a stack is first created, it contains no items.

 

Boolean empty()

E peek()

E pop()

E push(E item)

int search(Object o)