第四届蓝桥杯决赛题-九宫重排（双向广搜）.java

如下面第一个图的九宫格中，放着 1~8 的数字卡片，还有一个格子空着。与空格子相邻的格子中的卡片可以移动到空格中。经过若干次移动，可以形成第二个图所示的局面。

　　我们把第一个图的局面记为：12345678.
　　把第二个图的局面记为：123.46758
　　显然是按从上到下，从左到右的顺序记录数字，空格记为句点。
　　本题目的任务是已知九宫的初态和终态，求最少经过多少步的移动可以到达。如果无论多少步都无法到达，则输出-1。

/** 132757	张燚	九宫重排	  2014-03-08 21:56	5.209KB	JAVA	正确	 100	156ms	33.90MB	评测详情  * * */
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Queue;
public class Main{//双向广搜private static HashMap<String,Integer> hm1=null,hm2=null;public static void main(String[] args) {BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));try {String start=bf.readLine();String end=bf.readLine();char a[][]=new char[3][3];char b[][]=new char[3][3];int c=0;int x1=0,y1=0,x2=0,y2=0;for(int i=0;i<3;i++){for(int j=0;j<3;j++){a[i][j]=start.charAt(c);b[i][j]=end.charAt(c);if(a[i][j]=='.'){x1=i;y1=j;}if(b[i][j]=='.'){x2=i;y2=j;}c++;}}Node node1=new Node(a,0,x1,y1);Node node2=new Node(b,0,x2,y2);Queue<Node> q1=new LinkedList<Node>();Queue<Node> q2=new LinkedList<Node>();hm1=new HashMap<String, Integer>();hm2=new HashMap<String, Integer>();hm1.put(start, 0);hm2.put(end, 0);q1.add(node1);q2.add(node2);System.out.println(bfs(q1,q2));} catch (IOException e) {e.printStackTrace();}}private static int bfs(Queue<Node> q1,Queue<Node> q2) {while(!q1.isEmpty()||!q2.isEmpty()){if(!q1.isEmpty()){Node node1=q1.poll();//	System.out.println(node1.getTuString()+"----1");if(hm2.containsKey(node1.getTuString())){return node1.getSum()+hm2.get(node1.getTuString());}int x=node1.getX();int y=node1.getY();if(x>0){char a[][]=node1.getTuCopy();a[x][y]=a[x-1][y];a[x-1][y]='.';Node n=new Node(a,node1.getSum()+1,x-1,y);String s=n.getTuString();if(hm2.containsKey(s)){return n.getSum()+hm2.get(s);}if(!hm1.containsKey(s)){hm1.put(s, n.getSum());q1.add(n);}}if(x<2){char a[][]=node1.getTuCopy();a[x][y]=a[x+1][y];a[x+1][y]='.';Node n=new Node(a,node1.getSum()+1,x+1,y);String s=n.getTuString();if(hm2.containsKey(s)){return n.getSum()+hm2.get(s);}if(!hm1.containsKey(s)){hm1.put(s, n.getSum());q1.add(n);}}if(y>0){char a[][]=node1.getTuCopy();a[x][y]=a[x][y-1];a[x][y-1]='.';Node n=new Node(a,node1.getSum()+1,x,y-1);String s=n.getTuString();if(hm2.containsKey(s)){return n.getSum()+hm2.get(s);}if(!hm1.containsKey(s)){hm1.put(s, n.getSum());q1.add(n);}}if(y<2){char a[][]=node1.getTuCopy();a[x][y]=a[x][y+1];a[x][y+1]='.';Node n=new Node(a,node1.getSum()+1,x,y+1);String s=n.getTuString();if(hm2.containsKey(s)){return n.getSum()+hm2.get(s);}if(!hm1.containsKey(s)){hm1.put(s, n.getSum());q1.add(n);}}}if(!q2.isEmpty()){Node node2=q2.poll();//	System.out.println(node2.getTuString()+"----2");if(hm1.containsKey(node2.getTuString())){return node2.getSum()+hm1.get(node2.getTuString());}int x=node2.getX();int y=node2.getY();if(x>0){char a[][]=node2.getTuCopy();a[x][y]=a[x-1][y];a[x-1][y]='.';Node n=new Node(a,node2.getSum()+1,x-1,y);String s=n.getTuString();if(hm1.containsKey(s)){return n.getSum()+hm1.get(s);}if(!hm2.containsKey(s)){hm2.put(s, n.getSum());q2.add(n);}}if(x<2){char a[][]=node2.getTuCopy();a[x][y]=a[x+1][y];a[x+1][y]='.';Node n=new Node(a,node2.getSum()+1,x+1,y);String s=n.getTuString();if(hm1.containsKey(s)){return n.getSum()+hm1.get(s);}if(!hm2.containsKey(s)){hm2.put(s, n.getSum());q2.add(n);}}if(y>0){char a[][]=node2.getTuCopy();a[x][y]=a[x][y-1];a[x][y-1]='.';Node n=new Node(a,node2.getSum()+1,x,y-1);String s=n.getTuString();if(hm1.containsKey(s)){return n.getSum()+hm1.get(s);}if(!hm2.containsKey(s)){hm2.put(s, n.getSum());q2.add(n);}}if(y<2){char a[][]=node2.getTuCopy();a[x][y]=a[x][y+1];a[x][y+1]='.';Node n=new Node(a,node2.getSum()+1,x,y+1);String s=n.getTuString();if(hm1.containsKey(s)){return n.getSum()+hm1.get(s);}if(!hm2.containsKey(s)){hm2.put(s, n.getSum());q2.add(n);}}}}return -1;}
}
class Node{char tu[][]=new char[3][3];int sum=0;int x=0,y=0;public Node(char[][] tu, int sum, int x, int y) {super();this.tu = tu;this.sum = sum;this.x = x;this.y = y;}public char[][] getTuCopy() {char a[][]=new char[3][3];for(int i=0;i<3;i++)for(int j=0;j<3;j++)a[i][j]=tu[i][j];return a;}public String getTuString() {StringBuffer sb=new StringBuffer("");for(int i=0;i<3;i++)for(int j=0;j<3;j++)sb.append(tu[i][j]);return sb.toString();}public void setTu(char[][] tu) {this.tu = tu;}public int getSum() {return sum;}public void setSum(int sum) {this.sum = sum;}public int getX() {return x;}public void setX(int x) {this.x = x;}public int getY() {return y;}public void setY(int y) {this.y = y;}
}