最近，在就这斯坦福大学的公开课Programming Methodology学习Java。练习了课后的习题之余，自己也编写了一些简单的代码。贴在此处。

 

 

/* File name:factorial.java
 * Author: Huai Xiaowei
 * ---------------------
 * This method will help me to better understand what a method is for.
 * And how does the messege is delievred in method and function.*/

import acm.program.*;

public class factorial extends ConsoleProgram{
 public void run(){
  int n=readInt("Enter n:");
  for(int i=1;i<=n;i++){
   println(i+"! = "+factorial(i));
  }
 }
 
 //This is a method which calculates the factorial of a number.
 public int factorial(int i){
  int result=1;
  for(int j=1;j<=i;j++){
   result *= j;
  }
  return(result);
 }
}

 

 

/*File name: Combinations.java
 Author: Huai Xiaowei
 --------------------------------
 Using the factorial method to caculate the combinations*/

import acm.program.*;

public class Combinations extends factorial{
 public void run(){
  int n = readInt("Enter n:");
  int k = readInt("Enter k:");
  if(n < k) println("Error!");
  else println("C("+n+","+k+")="+(factorial(n)/(factorial(k)*factorial(n-k))));
 }
}

 

 

/* File: NeedleOfBuffon
 * Author: Huai Xiaowei @ Sun Yat-sen University
 * There is a famous experiment in the history of probability, which bears
 * the name of Buffon's needle.
 * You can find a bunch of material about this important trial.
 * Here we will simulate the process of throwing a needle on parallel lines.*/
import java.lang.*;
import acm.program.*;
import acm.util.*;

public class NeedleOfBuffon extends ConsoleProgram{
 
 /* GapWidth是两条平行线间的距离
  * NeedleLength是针的长度
  * These two parameters can be changed to whatever you want, as
  * long as NeedLength is less or equal to GapWidth.*/
 private static final double PI = 3.141592653589793;
 private static final double NeedleLength = 1.0;
 private static final double GapWidth = 3.0;
 
 /*To produce x and alpha randomly*/
 private RandomGenerator rgen = RandomGenerator.getInstance();
 
 /*x是针的中点到线的距离*/
 public void run(){
  int nCount = 0;
  int nThrow = readInt("Input the times you want to throw this needle:");
  for(int i=0;i<nThrow;i++){
   double x = rgen.nextDouble(0,GapWidth/2);
   double alpha = rgen.nextDouble(0, 180.0);
   alpha = alpha*PI/180.0;
   if(x <= NeedleLength*Math.sin(alpha)/2.0)nCount++; /*这时针落在线上*/
  }
  println("Times when needle is on a line："+nCount);
  /* l is the length of the needle,d is the distance between two lines
   * p=2*l/(Pi*d) */
  double mypi = 2.0*(double)nThrow*NeedleLength/(nCount*GapWidth);
  println("PI got by this method has a value of "+mypi);
 }
}

 

/* File name: gcd.java
 * Author: Huai Xiaowei @ Sun Yat-sen University
 * gcd is a short for Greatest Common Divisor
 * There are two algorithmic methods to get the gcd of two numbers
 * One is called the 'brute force' approach
 * The other is Euclid's algorithm.
 * I have to admit the wisdom of ancient Greeks!*/

import acm.program.*;
import java.lang.*;

public class gcd extends ConsoleProgram{
 public void run(){
  int n1 = readInt("Enter the 1st number:");
  int n2 = readInt("Enter the 2nd number:");
  int a = bruteForce(n1,n2);
  int b = EuclidAlgorithm(n1,n2);
  println(n1+","+n2+" have the greatest common divisor "+a+".(using bruteForce)");
  println(n1+","+n2+" have the greatest common divisor "+b+".(using EuclidAlgorithm)");
 }
 
 /* The brute force method to get gcd*/
 private int bruteForce(int n1, int n2){
  int guess = Math.min(n1, n2);
  while(true){
   if(n1%guess==0 && n2%guess==0) break;
   else guess--;
  }
  return guess;
 }
  
 /* The Acient's wisdom*/
 private int EuclidAlgorithm(int x, int y){
  int r = x % y;
  while(r != 0){
   x = y;
   y = r;
   r = x % y;
  }
  return y;
 }
}