三、栈

1、字符串的反转

import java.io.*;
class StackX
{
   private int maxSize;
   private char[] stackArray;
   private int top;
   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);
   }
}  

//==========================================================
class Reverser
{
   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;
  }  
} 

//==========================================================
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("") )        // quit if [Enter]
            break;
         Reverser theReverser = new Reverser(input);
         output = theReverser.doRev(); // use it
         System.out.println("Reversed: " + output);
       }
   } 

   public static String getString() throws IOException
   {
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader br = new BufferedReader(isr);
      String s = br.readLine();
      return s;
   }
}

2、括号匹配

// to run this program: C>java bracketsApp
import java.io.*;                 // for I/Oclass 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!='(') )
                     System.out.println("Error: "+ch+" at "+j);
               }
               else                        // prematurely empty
                  System.out.println("Error: "+ch+" at "+j);
               break;
            default: 
               break;
        }  // end switch
     }  // end for
     if( !theStack.isEmpty() )
         System.out.println("Error: missing right delimiter");
     else
    　　  System.out.println("Right");
      }  // 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;
         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

 

3、算式中缀转后缀

　input为中缀表达式，output为后缀表达式

   栈中会保存+-*/(，栈底优先级低，栈顶优先级高（不包括括号），在括号内栈底优先级低，栈顶优先级高

　遍历input，取某个值i。

　　　i为数字时，直接添加到ouput中。

　　　i为'('时，直接将i push到栈中。

　　　i为'+-*/'时，如果栈不为空，pop栈的值s。

　　　　 如果s是'('或s为'+-*/'且优先级小于i，则先把s push到栈中，再把i push到栈中。

　　 　　如果s为'+-*/'且优先级大于等于i，则将s添加到output中，继续pop栈的值比较，直到那个值m的

　　　　　　 优先级小于i或栈为空为止，最后将m push到栈中，再将i push到栈中。

　　　i为')'时，pop栈的值s

　　　　 如果s是'('，则什么也不做

　　　　 如果s值其它值，则添加到output中，继续pop栈的值，直到pop的值为'('。

// to run this program: C>java InfixApp
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); }

   public int size()         // return size
   { return top+1; }

   public char peekN(int n)  // return item at index n
      { return stackArray[n]; }

   public void displayStack(String s)
   {
     　 System.out.print(s);
     　 System.out.print("Stack (bottom-->top): ");
      　for(int j=0; j<size(); j++)
       {
        　System.out.print( peekN(j) );
        　System.out.print("");
       }
    　　System.out.println("");
   }
}  // end class StackX

//============================================================
class InToPost                  // infix to postfix conversion
 {
   private StackX theStack;
   private String input;
   private String output = "";
   public InToPost(String in)   // constructor
   {
   　　  input = in;
    　　 int stackSize = input.length();
    　　 theStack = new StackX(stackSize);
    }
//--------------------------------------------------------------
   public String doTrans()      // do translation to postfix
   {
      for(int j=0; j<input.length(); j++)      // for each char
      {
         char ch = input.charAt(j);            // get it
         theStack.displayStack("For "+ch+" "); // *diagnostic*
         switch(ch)
         {
            case '+':               // it's + or -
            case '-':
               gotOper(ch, 1);      // go pop operators
               break;               //   (precedence 1)
            case '*':               // it's * or /
            case '/':
               gotOper(ch, 2);      // go pop operators
               break;               //   (precedence 2)
            case '(':               // it's a left paren
               theStack.push(ch);   // push it
               break;
            case ')':               // it's a right paren
               gotParen(ch);        // go pop operators
               break;
            default:                // must be an operand
               output = output + ch; // write it to output
               break;
         }  // end switch
      }  // end for
      while( !theStack.isEmpty() )     // pop remaining opers
      {
         theStack.displayStack("While ");  // *diagnostic*
         output = output + theStack.pop(); // write to output
      }
      theStack.displayStack("End   ");     // *diagnostic*
      return output;                   // return postfix
  }  // end doTrans()
//--------------------------------------------------------------
   public  void gotOper(char opThis, int prec1)
   {                                // got operator from input
      while( !theStack.isEmpty() )
      {
         char opTop = theStack.pop();
         if( opTop == '(' )            // if it's a '('
         {
            　　theStack.push(opTop);      // restore '('
            　　break;
         }
         else                          // it's an operator
         {
            int prec2;                 // precedence of new op
            if(opTop=='+' || opTop=='-')  // find new op prec
               prec2 = 1;
            else
               prec2 = 2;
            if(prec2 < prec1)          // if prec of new op less
            {                       //    than prec of old
              　　 theStack.push(opTop);   // save newly-popped op
              　　 break;
            }
            else                       // prec of new not less
               output = output + opTop;  // than prec of old
          }  // end else (it's an operator)
      }  // end while
      theStack.push(opThis);           // push new operator
  }  // end gotOp()

   public  void gotParen(char ch)
   {                             // got right paren from input
      while( !theStack.isEmpty() )
      {
         char chx = theStack.pop();
         if( chx == '(' )           // if popped '('
            break;                  // we're done
         else                       // if popped operator
            output = output + chx;  // output it
       }  // end while
    }  // end popOps()
}  // end class InToPost

//===============================================================
class InfixApp
{
   public static void main(String[] args) throws IOException
   {
      String input, output;
      while(true)
      {
         System.out.print("Enter infix: ");
         System.out.flush();
         input = getString();         // read a string from kbd
         if( input.equals("") )       // quit if [Enter]
        　　  break;         
      　　InToPost theTrans = new InToPost(input);
      　　output = theTrans.doTrans(); // do the translation
      　　System.out.println("Postfix is " + output + '
');
       }  // 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 InfixApp

4、后缀表达式求值

操作数->入栈

操作符->从栈中提出两个操作数，用操作符将其执行运算。结果入栈。

// to run this program: C>java PostfixApp
import java.io.*;              // for I/Oclass StackX
   {
  　　 private int maxSize;
　　   private int[] stackArray;
 　　  private int top;
//--------------------------------------------------------------
   public StackX(int size)      // constructor
      {
     　　 maxSize = size;
     　　 stackArray = new int[maxSize];
    　　  top = -1;
      }
//--------------------------------------------------------------
   public void push(int j)     // put item on top of stack
      { stackArray[++top] = j; }
//--------------------------------------------------------------
   public int pop()            // take item from top of stack
      { return stackArray[top--]; }
//--------------------------------------------------------------
   public int peek()           // peek at top of stack
      { return stackArray[top]; }
//--------------------------------------------------------------
   public boolean isEmpty()    // true if stack is empty
      { return (top == -1); }
//--------------------------------------------------------------
   public boolean isFull()     // true if stack is full
      { return (top == maxSize-1); }
//--------------------------------------------------------------
   public int size()           // return size
      { return top+1; }
//--------------------------------------------------------------
   public int peekN(int n)     // peek at index n
      { return stackArray[n]; }
//--------------------------------------------------------------
   public void displayStack(String s)
      {
      System.out.print(s);
      System.out.print("Stack (bottom-->top): ");
      for(int j=0; j<size(); j++)
         {
         System.out.print( peekN(j) );
         System.out.print(' ');
         }
      System.out.println("");
      }
//--------------------------------------------------------------
   }  // end class StackXclass ParsePost
   {
   private StackX theStack;
   private String input;
//--------------------------------------------------------------
   public ParsePost(String s)
      { input = s; }
//--------------------------------------------------------------
   public int doParse()
      {
      theStack = new StackX(20);             // make new stack
      char ch;int num1, num2, interAns;
      for(int j=0; j<input.length(); j++)       // for each char,
         {
         　　ch = input.charAt(j);              // read from input
        　　 theStack.displayStack(""+ch+" ");  // *diagnostic*
        　　 if(ch >= '0' && ch <= '9')         // if it's a number
          　　  theStack.push( (int)(ch-'0') ); //   push it
      　　   else                               // it's an operator
          　　  {
          　　　　  num2 = theStack.pop();          // pop operands
           　　　　 num1 = theStack.pop();
          　　　　  switch(ch)                      // do arithmetic
             　　　　  {
             　　　　　　  case '+':
               　　　　  　　 interAns = num1 + num2;
                　　　　　　  break;
             　　　　　　  case '-':
                 　　　　　　 interAns = num1 - num2;
                 　　　　　　 break;
               　　　　　　case '*':
                 　　　　　　 interAns = num1 * num2;
                 　　　　　　 break;
               　　　　　　case '/':
                　　　　　　  interAns = num1 / num2;
                 　　　　　　 break;
              　　　　　　 default:
                　　　　　　  interAns = 0;
               }  // end switch
           　　 theStack.push(interAns);        // push result
            }  // end else
         }  // end for
      interAns = theStack.pop();            // get answer
      return interAns;
      }  // end doParse()
   }  // end class ParsePost
////////////////////////////////////////////////////////////////
class PostfixApp
{
   public static void main(String[] args) throws IOException
   {
      String input;
      int output;
      while(true)
      {
         System.out.print("Enter postfix: ");
       　System.out.flush();
         input = getString();         // read a string from kbd
       　if( input.equals("") )       // quit if [Enter]
        　　 break;
       　ParsePost aParser = new ParsePost(input);
       　output = aParser.doParse();  // do the evaluation
       　System.out.println("Evaluates to " + output);
      }  // 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 PostfixApp

5、栈的链表实现

// to run this program: C>java LinkStackApp
class Link
{
   public long dData;             // data item
   public Link next;              // next link in list
   public Link(long dd)           // constructor
   { dData = dd; }
   public void displayLink()      // display ourself
   { System.out.print(dData + " "); }
}

//==============================================================
class LinkList
{
   private Link first;            // ref to first item on list

   public LinkList()              // constructor
   { first = null; }           // no items on list yet

   public boolean isEmpty()       // true if list is empty
   { return (first==null); }

   public void insertFirst(long dd) // insert at start of list
   {                           // make new link
      Link newLink = new Link(dd);
      newLink.next = first;       // newLink --> old first
      first = newLink;            // first --> newLink
   }

   public Long deleteFirst()      // delete first item
   {                           // (assumes list not empty)
      if(!isEmpty())
      {
          Link temp = first;
          first = first.next;
          return temp.dData;
      }
      else
          return null;
   }

   public void displayList()
   {
      Link current = first;       // start at beginning of list
      while(current != null)      // until end of list,
      {
         current.displayLink();   // print data
         current = current.next;  // move to next link
      }
      System.out.println("");
   }
} 

//==============================================================
class LinkStack
{
   private LinkList theList;
   public LinkStack()             // constructor
   {
      theList = new LinkList();
   }
   public void push(long j)     // put item on top of stack
   {
      theList.insertFirst(j);
   }
   public Long pop()            // take item from top of stack
   {
      return theList.deleteFirst();
   }
   public boolean isEmpty()       // true if stack is empty
   {
      return ( theList.isEmpty() );
   }
   public void displayStack()
   {
      System.out.print("Stack (top-->bottom): ");
      theList.displayList();
   }
} 

//==============================================================
class LinkStackApp
{
   public static void main(String[] args)
   {
      LinkStack theStack = new LinkStack(); // make stack

      theStack.push(20);                    // push items
      theStack.push(40);

      theStack.displayStack();              // display stack

      theStack.push(60);                    // push items
      theStack.push(80);

      theStack.displayStack();              // display stack

      theStack.pop();                       // pop items
      theStack.pop();

      theStack.displayStack();              // display stack
   }
}