數據結構與算法19-迭代器-遞歸

時間  2019-11-13
標籤 數據 結構 算法 迭代 遞歸 欄目 應用數學 简体版
原文   原文鏈接

 以用戶交互的形式呈現迭代器的功能，迭代器更加靈活的對鏈表進行增刪改查。java

迭代器上刪除一項後，要將指針放到後一項，不能放在前一項。執行插入方法後，將current指向新插入的鏈結點。this

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Link
{
	public Link next;
	public long ddata;
	public Link(long dd)
	{
		ddata = dd;
	}
	public void displayLink()
	{
		System.out.print(ddata+" ");
	}
}
class LinkList
{
	private Link first;
	public LinkList()
	{
		first = null;
	}
	public Link getFirst()
	{
		return first;
	}
	public void setFirst(Link f)
	{
		first = f;
	}
	public boolean isEmpty()
	{
		return first == null;
	}
	public ListIterator getIterator(){
		return new ListIterator(this);
	}
	public void displayList()
	{
		Link current = first;
		while(current != null)
		{
			current.displayLink();
			current = current.next;
		}
		System.out.println(" ");
	}
}
class ListIterator
{
	private Link current;
	private Link previous;
	private LinkList ourList;
	public ListIterator(LinkList list)
	{
		ourList = list;
		reset();
	}
	public void reset()
	{
		current = ourList.getFirst();
		previous = null;
	}
	public boolean atEnd()
	{
		return (current.next==null);
	}
	public void nextLink()
	{
		previous = current;
		current = current.next;
	}
	public Link getCurrent()
	{
		return current;
	}
	public void insertAfter(long dd)
	{
		Link newLink = new Link(dd);
		if(ourList.isEmpty())
		{
			ourList.setFirst(newLink);
			current = newLink;
		}
		else
		{
			newLink.next = current.next;
			current.next = newLink;
			nextLink();
		}
	}
	public void insertBefore(long dd)
	{
		Link newLink = new Link(dd);
		if(previous == null)
		{
			newLink.next = ourList.getFirst();
			ourList.setFirst(newLink);
			reset();
		}
		else
		{
			newLink.next = previous.next;
			previous.next = newLink;
			current = newLink;
		}
	}
	public long deleteCurrent()
	{
		long value = current.ddata;
		if(previous == null)
		{
			ourList.setFirst(current.next);
			reset();
		}
		else
		{
			previous.next = current.next;
			if(atEnd())
				reset();
			else
				current = current.next;
		}
		return value;
		
	}
}
class InterItarApp
{
public static void main(String[] args) throws IOException
{
	LinkList theList = new LinkList();
	ListIterator iter1 = theList.getIterator();
	long value;
	iter1.insertAfter(20);
	iter1.insertAfter(40);
	iter1.insertAfter(80);
	iter1.insertBefore(60);
	while(true)
	{
		System.out.print("enter first letter of show,reset, ");
		System.out.print("next,get,before,after,delete：");
		System.out.flush();
		int choice = getChar();
		switch(choice)
		{
		case 's':
			if(!theList.isEmpty())
				theList.displayList();
			else
				System.out.println("list is empty");
			break;
		case 'r':
			iter1.reset();
			break;
		case 'n':
			if(!theList.isEmpty()&&!iter1.atEnd())
				iter1.nextLink();
			else
				System.out.println("can't go to next link");
			break;
		case 'g':
			if(!theList.isEmpty())
			{
				value = iter1.getCurrent().ddata;
				System.out.println("returned "+value);
			}
			else
				System.out.println("list is empty");
			break;
		case 'b':
			System.out.print("enter value to insert: ");
			System.out.flush();
			value = getInt();
			iter1.insertBefore(value);
			break;
		case 'a':
			System.out.print("enter value to insert: ");
			System.out.flush();
			value = getInt();
			iter1.insertAfter(value);
			break;
		case 'd':
			if(!theList.isEmpty())
			{
				value = iter1.deleteCurrent();
				System.out.println("deleted "+ value);
			}
			else
				System.out.println("can't delete");
			default:
				System.out.println("invalid entry");
			
		}
	}
	
}
private static long getInt() throws IOException {
	String s = getString();
	return Integer.parseInt(s);
}
private static String getString() throws IOException{
	InputStreamReader isr = new InputStreamReader(System.in);
	BufferedReader br = new BufferedReader(isr);
	String s = br.readLine();
	return s;
}
private static int getChar() throws IOException {
	String s = getString();
	return s.charAt(0);
}

}
enter first letter of show,reset, next,get,before,after,delete：s
20 40 60 80  
enter first letter of show,reset, next,get,before,after,delete：r
enter first letter of show,reset, next,get,before,after,delete：n
enter first letter of show,reset, next,get,before,after,delete：n
enter first letter of show,reset, next,get,before,after,delete：g
returned 60
enter first letter of show,reset, next,get,before,after,delete：b
enter value to insert: 55
enter first letter of show,reset, next,get,before,after,delete：a
enter value to insert: 77
enter first letter of show,reset, next,get,before,after,delete：s
20 40 55 77 60 80  
enter first letter of show,reset, next,get,before,after,delete：
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class TriangleApp
{
	static int theNumber;
	public static void main(String[] args) throws IOException
	{
		System.out.print("enter a number: ");
		theNumber = getInt();//將getInt獲得的s賦值給theNumber
		int theAnswer = triangle(theNumber);//將triangle中獲得的theNumber賦值給theAnswer
		System.out.println("Triangle=" + theAnswer);//輸出theAnswer
	}
	public static int triangle(int n)
	{
		if(n==1)                //若是n=1
			return 1;           //返回1
		else                          
			return(n+triangle(n-1));    //不然返回n+triangle的n-1的結果
	}
	
	public static int getInt() throws IOException
	{
		String s = getString();           //getString的值賦值給s
		return Integer.parseInt(s);        //返回給s
	}
	public static String getString() throws IOException
	{
		InputStreamReader isr = new InputStreamReader(System.in);   //創建輸入的isr
		BufferedReader br = new BufferedReader(isr);                //將isr輸入br中
		String s = br.readLine();                                   //將br輸入s
		return s;                                                   //返回s
	}
}
enter a number: 555
Triangle=154290

調用遞歸方法，本身調用本身指針

如下爲詳細過程code

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class TriangleApp
{
	static int theNumber;
	public static void main(String[] args) throws IOException
	{
		System.out.print("enter a number: ");
		theNumber = getInt();
		int theAnswer = triangle(theNumber);
		System.out.println("Triangle=" + theAnswer);
	}
	public static int triangle(int n)
	{
		System.out.println("enter:n=" + n);
		if(n==1)
		{
			System.out.println("returning 1");
			return 1;
		}
		else
		{
			int temp = n + triangle(n-1);
			System.out.println("returning "+temp);
			return temp;
		}
	}
	
	public static int getInt() throws IOException
	{
		String s = getString();
		return Integer.parseInt(s);
	}
	public static String getString() throws IOException
	{
		InputStreamReader isr = new InputStreamReader(System.in);
		BufferedReader br = new BufferedReader(isr);
		String s = br.readLine();
		return s;
	}
}

 triangle()方法調用自身時，它的參數從10開始，每次減一，這個發那個發反覆進入自身，直到方法的參數減少到1，因而方法返回，這會引起一系列的返回序列。這個方法向鳳凰涅盤同樣的返回，脫離被放棄的那一層，每當返回時，這個方法把調用它的參數n與其調用下一層方法的返回值相加。遞歸

注意：在最內層返回1以前，實際上在同一時刻有10個不一樣的triangle()方法實例存在，最外層傳入的參數是10，最內層傳入的參數是1.get

enter a number: 10
enter:n=10
enter:n=9
enter:n=8
enter:n=7
enter:n=6
enter:n=5
enter:n=4
enter:n=3
enter:n=2
enter:n=1
returning 1
returning 3
returning 6
returning 10
returning 15
returning 21
returning 28
returning 36
returning 45
returning 55
Triangle=55

基於循環的方法效率更高input

變位數it

輸入一個單詞，將字母進行排列，將全部結果都排列組合出來；io

利用遞歸，從第一個單詞開始向右移動，每兩個字母換一次位置，直到將全部可能都列出。class

doAnagram()每次調用本身的時候，詞的大小都減小一個字母，而且開始i的位置向右移動一位。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


class AnagramApp {
	static int size;
	static int count;
	static char[] arrChar = new char[100];
	public static void main(String[] args) throws IOException
	{
		System.out.print("enter a word: ");
		String input = getString();
		size = input.length();
		count = 0;
		for(int j=0;j<size;j++)
		arrChar[j] = input.charAt(j);
		doAnagram(size);
	}
	private static void doAnagram(int newSize) {
		// TODO Auto-generated method stub
		if(newSize==1)
			return;
		for(int j=0;j<newSize;j++)
		{
			doAnagram(newSize-1);
			if(newSize==2)
				displayWord();
			rotate(newSize);
		}
	}
	private static void rotate(int newSize) {
		// TODO Auto-generated method stub
		int j;
		int position = size - newSize;
		char temp = arrChar[position];
		for(j=position+1;j<size;j++)
		{
			arrChar[j-1] = arrChar[j];
			arrChar[j] = temp;
		}
	}
	private static void displayWord() {
		// TODO Auto-generated method stub
		if(count < 99)
			System.out.print(" ");
		if(count < 9)
			System.out.print(" ");
		System.out.print(++count+" ");
		for(int j=0;j<size;j++)
			System.out.print(arrChar[j]);
		System.out.print(" ");
		System.out.flush();
		if(count%6==0)
			System.out.println("");
	}
	private static String getString() throws IOException {
		// TODO Auto-generated method stub
		InputStreamReader isr = new InputStreamReader(System.in);
		BufferedReader br = new BufferedReader(isr);
		String s = br.readLine();
		return s;
	}
}
enter a word: dog
  1 dog   2 dgo   3 ogd   4 odg   5 gdo   6 god
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