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| import java.io.*; // for I/O
class Params //这个类的对象被压入栈中
{
public int n; //用来存放键盘输入的数字
public int returnAddress; //返回的地址
public Params(int nn, int ra)
{
n=nn;
returnAddress=ra;
}
} // end class Params
class StackX
{
private int maxSize; // size of StackX array
private Params[] stackArray;
private int top; // top of stack
//--------------------------------------------------------------
public StackX(int s) // constructor
{
maxSize = s; // set array size
stackArray = new Params[maxSize]; // create array
top = -1; // no items yet
}
//--------------------------------------------------------------
public void push(Params p) // put item on top of stack
{
stackArray[++top] = p; // increment top, insert item
}
//--------------------------------------------------------------
public Params pop() // take item from top of stack
{
return stackArray[top--]; // access item, decrement top
}
//--------------------------------------------------------------
public Params peek() // peek at top of stack
{
return stackArray[top];
}
//--------------------------------------------------------------
} // end class StackX
class stackTriangle
{
static int theNumber; //用于接收输入的int
static int theAnswer;
static StackX theStack;
static int codePart; //用于switch选择
static Params theseParams;
public static void main(String[] args) throws IOException
{
System.out.print("Enter a number: ");
theNumber = getInt(); //接收键盘输入的int
recTriangle();
System.out.println("Triangle="+theAnswer);
} // end main()
public static void recTriangle()
{
theStack = new StackX(10000);
codePart = 1;
while( step() == false) // call step() until it's true
; // null statement
}
//-------------------------------------------------------------
public static boolean step()
{
switch(codePart)
{
case 1: // initial call
System.out.println("进入1");
theseParams = new Params(theNumber, 6);
theStack.push(theseParams);
codePart = 2;
break;
case 2: // method entry
System.out.println("进入2");
theseParams = theStack.peek(); //对输入的数字一直减1，直到等于1，如果大于1就跳到3中，压入栈中
if(theseParams.n == 1) // n是键盘输入的数字，如果是1，结果是1，codePart跳到5
{
theAnswer = 1;
codePart = 5; // exit
}
else //如果大于1，就跳到3
codePart = 3; // recursive call
break;
case 3:
System.out.println("进入3");
Params newParams = new Params(theseParams.n - 1, 4);
theStack.push(newParams); //把输入的数字减去1，并压入栈中
codePart = 2; //回到2中判断数组减去1后，是否等于1
break;
case 4: // calculation
System.out.println("进入4");
theseParams = theStack.peek(); //取得2
theAnswer = theAnswer + theseParams.n; //1+2
codePart = 5;
break;
case 5: // method exit
System.out.println("进入5");
theseParams = theStack.peek();
codePart = theseParams.returnAddress; //在2和3中交替跳转后，结束时跳到5，此时栈中codePart除了栈底是6，其他都是4
theStack.pop(); //在取得了下次跳转的位置后，出栈，第一次出栈的是（1,4）
break;
case 6: // return point
System.out.println("进入6");
return true;
} // end switch
return false;
} // end triangle
public static String getString() throws IOException
{
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String s = br.readLine();
return s;
}
public static int getInt() throws IOException
{
String s = getString();
return Integer.parseInt(s);
}
}
|
