java基础：18.1 递归

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之前学C语言时对递归有了较多了解，这部分主要把题目的代码都自己实现一遍。知识点不再记录了

import java.io.File;
import java.util.Scanner;

public class ComputeFactorial {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		String directory = "f:\\java";
		System.out.println(getSize(new File(directory)) + " bytes") ;
		
		double [] list = { 2.5,1,5,8,3.1,5.5,6.8};
		recursionSort(list);
		for (double e:list)
			   System.out.println(e);  
		System.out.println("key = 3.1 , after BinarySearch fine the index = " + recursiveBinarySearch(list,3.1) );
		String s = "II I";
		System.out.println(" \""+s +" \" is isPalindrome = " + isPalindrome(s));
		int fibonacci_index = 10;
		System.out.println(" while index = " + fibonacci_index + " ,the fibonacci data = " + fibonacci(fibonacci_index));
		int factorialN = 5;
		System.out.println(" while N = " + factorialN + " ,the factorial result = " + factorial(factorialN));		
	}
	
	private static long getSize(File file) {
		long size = 0;
		
		if (file.isDirectory()) {
			File[] files = file.listFiles();
			for (int i = 0; files != null && i < files.length; i++)
				size += getSize(files[i]);
		}
		else  size += file.length();
	
		return size;
	}

	public static int recursiveBinarySearch(double []list, double key) {
		int low = 0;
		int high = list.length-1;
		return recursiveBinarySearch(list,low,high,key);
	}
	private static int recursiveBinarySearch(double []list, int low, int high, double key) {
		if (low > high) return -low-1;
		int mid = (low+high)/2;
		if(key < list[mid]) 
			return recursiveBinarySearch(list,low,mid-1,key);
		else if(key > list[mid])
			return recursiveBinarySearch(list,mid+1,high,key);
		else
		    return mid ;
	}
	
	
	/* --------  sort  ------- */
	public static void recursionSort(double []list) {
		recursionSort(list,0,list.length-1);
	}
	
	private static void recursionSort(double []list,int low,int high) {
		if(low<high) {
			int indexMin = low;
			double min = list[low];
			for(int i = low+1;  i<= high; i++) {
				if(list[i] < min) {
					min = list[i];
					indexMin = i;
				}
			}
			list[indexMin] = list[low];
			list[low] = min;
			
			recursionSort(list,low+1,high);
		}
	}
	
	/* ---  isPalindrome  --- */
	public static boolean isPalindrome(String s) {
		return isPalindrome(s,0,s.length()-1);
	}
	private static boolean isPalindrome(String s,int low,int high) {
		if(low>= high) return true;
		else if(s.charAt(low) != s.charAt(high)) 
			 return false;
		else return isPalindrome(s,low+1,high-1);
	}
	
	/* ---  fibonacci  --- */
	public static int fibonacci(int index) {
		if(index==0) return 0;
		else	if(index==1) return 1;
		else return fibonacci(index-1)+fibonacci(index-2);
	}
	
	/* ---  factorial  --- */
	public static long factorial(int n) {
			if(n==0)  return 1;
		else return n*factorial(n-1);
		
	}

}

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