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
////////////////////////////////////////////////////////////////