回溯法簡介及示例

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.StringTokenizer;

class InterSection{  //路口類
	int left;  //向左方向
	int forward;  //向前方向
	int right;  //向右方向
}

public class Maze {
	int mazeSize;  //路口個數
	InterSection[] intSec;  //路口集合
	int exit;  //出口
	
	Maze(String fileName) {
		String line;

		try{
			BufferedReader in = new BufferedReader(new FileReader(fileName));
			line = in.readLine();  //讀檔案的第1行
			mazeSize = Integer.parseInt(line.trim());  //去空格並轉換型別
			intSec = new InterSection[mazeSize + 1];
			
			for ( int i = 1 ; i <= mazeSize ; i ++ ) {  //讀檔案的後續行
				line = in.readLine();
				StringTokenizer tokenizer = new StringTokenizer(line);  //把當前行數值轉換成StringTokenizer物件
				InterSection curr = new InterSection();
				curr.left = Integer.parseInt(tokenizer.nextToken());
				curr.forward = Integer.parseInt(tokenizer.nextToken());
				curr.right = Integer.parseInt(tokenizer.nextToken());
				intSec[i] = curr;
			}
			exit = Integer.parseInt(in.readLine());
			in.close();
		}
		catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public boolean travMaze(int intSecValue) {  //搜尋
	//用回朔法搜尋迷宮的所有分支，intSexValue為當前所處路口號
	//當搜尋到出口時函式返回1，否則返回0
		if (intSecValue > 0) {
			if (intSecValue == exit) {  //搜尋成功出口
				System.out.print(intSecValue + "<==");
				return true;
			}
			
			else if (travMaze(intSec[intSecValue].left)) {  //向當前路口的左分支探索
				System.out.print(intSecValue + "<==");
				return true;
			}
			
			else if (travMaze(intSec[intSecValue].forward)) {  //向當前路口的前分支探索
				System.out.print(intSecValue + "<==");
				return true;
			}
			
			else if (travMaze(intSec[intSecValue].right)) {  //向當前路口的右分支探索
				System.out.print(intSecValue + "<==");
				return true;
			}
		}
		
		return false;  //搜尋失敗出口
		
	}
	
	public static void main(String[] args) {
		String fileName = "F:\\Maze.txt";
		Maze m = new Maze(fileName);
		int start = 1;
		
		if (m.travMaze(start)) {
			System.out.println();
			System.out.println("此迷宮的一條通路如上所示");
		}
		else {
			System.out.println("此迷宮無通路出來！");
		}
	}
	
}
 

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