使用DFS解決8益智遊戲

Question

我正試圖解決DFS從用BFS實現的此代碼開始的8益智問題。做這件事最簡單的方法是什麼？我研究過的所有代碼都是工作和不完整的，這使我陷入了比以前更加混亂的境地。

import java.util.HashMap; 
import java.util.LinkedList; 
import java.util.Map; 
import java.util.Queue; 

class EightPuzzle { 

Queue<String> agenda = new LinkedList<String>(); // Use of Queue Implemented using LinkedList for Storing All the Nodes in BFS. 
Map<String,Integer> stateDepth = new HashMap<String, Integer>(); // HashMap is used to ignore repeated nodes 
Map<String,String> stateHistory = new HashMap<String,String>(); // relates each position to its predecessor 

public static void main(String args[]){ 

    String str="087465132";         // Input the Board State as a String with 0 as the Blank Space 

    EightPuzzle e = new EightPuzzle();    // New Instance of the EightPuzzle 
    e.add(str, null);             // Add the Initial State 

    while(!e.agenda.isEmpty()){ 
     String currentState = e.agenda.remove(); 
     e.up(currentState);          // Move the blank space up and add new state to queue 
     e.down(currentState);          // Move the blank space down 
     e.left(currentState);          // Move left 
     e.right(currentState);       // Move right and remove the current node from Queue 
    } 

    System.out.println("Solution doesn't exist"); 
} 

//Add method to add the new string to the Map and Queue 
void add(String newState, String oldState){ 
    if(!stateDepth.containsKey(newState)){ 
     int newValue = oldState == null ? 0 : stateDepth.get(oldState) + 1; 
     stateDepth.put(newState, newValue); 
     agenda.add(newState); 
     stateHistory.put(newState, oldState); 
    } 
} 

/* Each of the Methods below Takes the Current State of Board as String. Then the operation to move the blank space is done if possible. 
    After that the new string is added to the map and queue.If it is the Goal State then the Program Terminates. 
*/ 
void up(String currentState){ 
    int a = currentState.indexOf("0"); 
    if(a>2){ 
     String nextState = currentState.substring(0,a-3)+"0"+currentState.substring(a-2,a)+currentState.charAt(a-3)+currentState.substring(a+1); 
     checkCompletion(currentState, nextState); 
    } 
} 

void down(String currentState){ 
    int a = currentState.indexOf("0"); 
    if(a<6){ 
     String nextState = currentState.substring(0,a)+currentState.substring(a+3,a+4)+currentState.substring(a+1,a+3)+"0"+currentState.substring(a+4); 
     checkCompletion(currentState, nextState); 
    } 
} 
void left(String currentState){ 
    int a = currentState.indexOf("0"); 
    if(a!=0 && a!=3 && a!=6){ 
     String nextState = currentState.substring(0,a-1)+"0"+currentState.charAt(a-1)+currentState.substring(a+1); 
     checkCompletion(currentState, nextState); 
    } 
} 
void right(String currentState){ 
    int a = currentState.indexOf("0"); 
    if(a!=2 && a!=5 && a!=8){ 
     String nextState = currentState.substring(0,a)+currentState.charAt(a+1)+"0"+currentState.substring(a+2); 
     checkCompletion(currentState, nextState); 
    } 
} 

private void checkCompletion(String oldState, String newState) { 
    add(newState, oldState); 
    if(newState.equals("123456780")) { 
     System.out.println("Solution Exists at Level "+stateDepth.get(newState)+" of the tree"); 
     String traceState = newState; 
     while (traceState != null) { 
      System.out.println(traceState + " at " + stateDepth.get(traceState)); 
      traceState = stateHistory.get(traceState); 
     } 
     System.exit(0); 
    } 
} 

} 

Answer 1

DFS是不是爲了解決8拼圖，但

與該代碼的最佳方式，你應該能夠僅通過改變主要方法，nextState並增加了實現它爲DFS goDepth方法。

我建議分析一下這段代碼，然後試着想象它在紙上的工作原理。在你完全理解它是如何工作的之後，你可以在其中實現DFS算法。