Question

我正在尝试用从BFS实现的代码开始解决DFS的8-puzzle问题。这样做最简单的方法是什么？我研究过的所有代码都是工作和不完整的，这使我比以前更容易陷入混乱。

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不是解决8-puzzle的最佳方法，但

使用该代码，您应该能够通过仅更改main方法，nextState和添加goDepth方法将其实现为DFS。

我建议分析此代码，然后尝试可视化它在纸上的工作方式。在确切了解它是如何工作之后，您可以在其中实现DFS算法而不会出现问题。

使用DFS解决8-puzzle游戏

1 个答案: