import java.applet.*;
import java.awt.*;
import java.io.*;

public class PascalTriangle extends Applet {
  TextField ROW;
  TextArea DISPLAY;

  public static void main(String args[]) {
    PascalTriangle pt = new PascalTriangle();
    Frame appletFrame = new Frame("Pascal Triangle");
    appletFrame.add("Center",pt);
    appletFrame.setSize(500,300);
    appletFrame.setLocation(50,50);
    pt.init();
    pt.start();
    appletFrame.show();
  }

  public void printOut(String s) {
    int maxDig=0; // number of digits in biggest number in triangle
    int curDig=0; // number of digits in current element
    long result=0; // the value of the entry

    int num = Integer.parseInt(s);
    DISPLAY.appendText("\n"+s+" Rows of Pascal's Triangle:  \n\n");
    // This is a crude hack to fix formatting.
    maxDig=getDigits(calcEntry(num-1,(num-1)/2));
    if((maxDig+2)%2 != 1) { // if even number
      maxDig++; // make odd
    }

    // Start for-loops to print out the triangle
    for(int i=0;i<num;i++) { // rows
      for(int j=0;j<=i;j++) { // elements
	result=calcEntry(i,j);
	curDig=getDigits(result); // digits in current entry
	if(j==0) { // if this is the first element in the row
	  for(int k=num;k>i;k--) {
	    for(int a=maxDig/2;a>=0;a--) {
	      DISPLAY.appendText(" ");  // spaces in front of first element
	    }
	  }
	}
	DISPLAY.appendText(Long.toString(result));
	if(i!=0) { // after first row
	  for(int a=maxDig-curDig;a>=0;a--) { // fewer digits in current entry means more spaces
	    DISPLAY.appendText(" "); // spaces between two elements
	  }
	}
      } // end of elements (one row)
      DISPLAY.appendText("\n");
    } // end of all rows
  } // end printOut method

  public long calcEntry(int row,int element) {
    if(element == 0 || element == row) {
      return 1;
    }
    else if(row < 21) {
      return(doFactorial(row)/(doFactorial(element)*doFactorial(row-element)));
    }
    else {
      return(calcEntry(row-1,element-1)+calcEntry(row-1,element));
    }
  }

  public long doFactorial(int num) {
    if(num==0 || num==1) {
      return 1;
    }
    else {
      return(num*doFactorial(num-1));
    }
  }

  /**
     This returns how many digits a (long) number has.
  */
  public int getDigits(long result) {
    String stringNum=Long.toString(result);
    return(stringNum.length());
  }

  public boolean action(Event e, Object o) {
    if(e.target instanceof Button) {
      printOut(ROW.getText());
      return true;
    }
    else {
      return false;
    }
  }

  public void init() {
    Font font = new Font("fixed",1,10);
    setLayout(new BorderLayout());
    DISPLAY = new TextArea(20,100);
    add("Center", DISPLAY);
    if(font.getName() != "fixed") {
      Font font2 = new Font("Courier",1,10);
      DISPLAY.setFont(font2);
    }
    else {
      DISPLAY.setFont(font);
    }

    Panel SouthPanel = new Panel();
    Panel NorthPanel = new Panel();
    NorthPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
    NorthPanel.add("North",new Label("Rows: "));
    ROW = new TextField(10);
    NorthPanel.add("North",ROW);
    NorthPanel.add(new Button("Do it"));
    add("South",SouthPanel);
    add("North",NorthPanel);
  }
} // end class