栈结构应用的两个实例

两个实例来自Java数据结构和算法.（第二版）第四章

1、单词逆序。

 要求从控制台读入一串字符，按回车结束输入，同时显示其逆序字符串。

对于颠倒顺序的操作，用栈来解决是很方便的。具体思想是把字符串中的每一个字符按顺序存入栈中，然后再一个一个的从栈中取出。这时就是按照逆序取出的字符串。    

// reverse.java
// stack used to reverse a string
// to run this program: C>java ReverseApp
import java.io.*;                 // for I/O
////////////////////////////////////////////////////////////////
class StackX//定义了栈的基本结构和操作
   {
   private int maxSize;//栈最大值
   private char[] stackArray;//栈内用数组存储数据
   private int top;//当前栈顶标号，从0开始
//--------------------------------------------------------------
   public StackX(int max)    // constructor
      {
      maxSize = max;
      stackArray = new char[maxSize];
      top = -1;
      }
//--------------------------------------------------------------
   public void push(char j)  // put item on top of stack
      {
      stackArray[++top] = j;
      }
//--------------------------------------------------------------
   public char pop()         // take item from top of stack
      {
      return stackArray[top--];
      }
//--------------------------------------------------------------
   public char peek()        // peek at top of stack
      {
      return stackArray[top];
      }
//--------------------------------------------------------------
   public boolean isEmpty()  // true if stack is empty
      {
      return (top == -1);
      }
//--------------------------------------------------------------
   }  // end class StackX
////////////////////////////////////////////////////////////////
class Reverser//封装了单词逆序的操作
   {
   private String input;                // input string
   private String output;               // output string
//--------------------------------------------------------------
   public Reverser(String in)           // constructor
      { input = in; }
//--------------------------------------------------------------
   public String doRev()                // reverse the string
      {
      int stackSize = input.length();   // get max stack size
      StackX theStack = new StackX(stackSize);  // make stack

      for(int j=0; j<input.length(); j++)
         {
         char ch = input.charAt(j);     // get a char from input
         theStack.push(ch);             // push it
         }
      output = "";
      while( !theStack.isEmpty() )
         {
         char ch = theStack.pop();      // pop a char,
         output = output + ch;          // append to output
         }
      return output;
      }  // end doRev()
//--------------------------------------------------------------
   }  // end class Reverser
////////////////////////////////////////////////////////////////
class ReverseApp
   {
   public static void main(String[] args) throws IOException
      {
      String input, output;
      while(true)
         {
         System.out.print("Enter a string: ");
         System.out.flush();
         input = getString();          // read a string from kbd
         if( input.equals("") )        // 若没有输入字符串直接按回车，则结束
            break;
                                       // make a Reverser
         Reverser theReverser = new Reverser(input);
         output = theReverser.doRev(); // use it
         System.out.println("Reversed: " + output);
         }  // end while
         System.out.println("this is end");
      }  // end main()
//--------------------------------------------------------------
   public static String getString() throws IOException
      {
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader br = new BufferedReader(isr);
      String s = br.readLine();
      return s;
      }
//--------------------------------------------------------------
   }  // end class ReverseApp
////////////////////////////////////////////////////////////////

2.分隔符匹配

有些分割符在编程中一定是成对出现的，例如（），{}，和[]等。如果发现有未匹配的分隔符，编译器会报错。因为匹配操作采取就近原则，后输入的分割符优先匹配，具有“后进先出”的特点。这个匹配操作可以用栈来实现。

具体操作是在输入过程中，如果遇到左匹配符，则将左匹配符压入栈中。如果遇到右匹配符，则从栈中取出一个数据，分析其与右匹配符是否相匹配。若匹配，则继续进行，若不匹配，则报错终止。

// brackets.java
// stacks used to check matching brackets
// to run this program: C>java bracketsApp
import java.io.*;                 // for I/O
////////////////////////////////////////////////////////////////
class StackX
   {
   private int maxSize;
   private char[] stackArray;
   private int top;
//--------------------------------------------------------------
   public StackX(int s)       // constructor
      {
      maxSize = s;
      stackArray = new char[maxSize];
      top = -1;
      }
//--------------------------------------------------------------
   public void push(char j)  // put item on top of stack
      {
      stackArray[++top] = j;
      }
//--------------------------------------------------------------
   public char pop()         // take item from top of stack
      {
      return stackArray[top--];
      }
//--------------------------------------------------------------
   public char peek()        // peek at top of stack
      {
      return stackArray[top];
      }
//--------------------------------------------------------------
   public boolean isEmpty()    // true if stack is empty
      {
      return (top == -1);
      }
//--------------------------------------------------------------
   }  // end class StackX
////////////////////////////////////////////////////////////////
class BracketChecker
   {
   private String input;                   // input string
//--------------------------------------------------------------
   public BracketChecker(String in)        // constructor
      { input = in; }
//--------------------------------------------------------------
   public void check()
      {
      int stackSize = input.length();      // get max stack size
      StackX theStack = new StackX(stackSize);  // make stack

      for(int j=0; j<input.length(); j++)  // get chars in turn
         {
         char ch = input.charAt(j);        // get char
         switch(ch)
            {
            case '{':                      // opening symbols
            case '[':
            case '(':
               theStack.push(ch);          // push them
               break;

            case '}':                      // closing symbols
            case ']':
            case ')':
               if( !theStack.isEmpty() )   // if stack not empty,
                  {
                  char chx = theStack.pop();  // pop and check
                  if( (ch=='}' && chx!='{') ||
                      (ch==']' && chx!='[') ||
                      (ch==')' && chx!='(') )//分隔符不匹配
                     System.out.println("Error: "+ch+" at "+j);
                  }
               else                        // prematurely empty
                  System.out.println("Error: "+ch+" at "+j);
               break;
            default:    // no action on other characters
               break;
            }  // end switch
         }  // end for
      // at this point, all characters have been processed
      if( !theStack.isEmpty() )
         System.out.println("Error: missing right delimiter");
      }  // end check()
//--------------------------------------------------------------
   }  // end class BracketChecker
////////////////////////////////////////////////////////////////
class BracketsApp
   {
   public static void main(String[] args) throws IOException
      {
      String input;
      while(true)
         {
         System.out.print(
                      "Enter string containing delimiters: ");
         System.out.flush();
         input = getString();     // read a string from kbd
         if( input.equals("") )   // quit if [Enter]
            break;
                                  // make a BracketChecker
         BracketChecker theChecker = new BracketChecker(input);
         theChecker.check();      // check brackets
         }  // end while
      }  // end main()
//--------------------------------------------------------------
   public static String getString() throws IOException
      {
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader br = new BufferedReader(isr);
      String s = br.readLine();
      return s;
      }
//--------------------------------------------------------------
   }  // end class BracketsApp
////////////////////////////////////////////////////////////////