Link to the original question http://poj.org/problem?id=1077
The general idea of the question is to turn the Jiugongge you input into the target Jiugongge (probably played this kind of game when I was young, and restore the Jiugongge), and then output the direction of each movement . If you don’t know Cantor’s development, you can Baidu it, it’s very useful for judging the weight of the whole arrangement. When submitting, c++ has been timed out, and it still doesn't work after changing it. It's ac after changing it to g++, which is depressed.
The code is as follows (with solution)
#include<iostream>
#include<queue>
#include<cstring>
#include<stdio.h>
using namespace std;
const int Len = 362880;//一共有9！种全排列
struct node{
int state[9];
int count;//记录步数
char d[100];//记录每一步的方向
};
int vis[Len] = {
0};//0表示第Len种情况还没出现过
int start[9];
int goal[9] = {
1,2,3,4,5,6,7,8,0};
int dir[4][2] = {
//4个方向
{
0,-1},//up
{
1,0},//right
{
0,1},//down
{
-1,0}//left
};
long int factory[] = {
1,1,2,6,24,120,720,5040,40320,362880};//康托展开常用阶乘
bool Cantor(int str[], int n){
//康托展开，判重
long result = 0;
for(int i = 0; i<n; i++){
int count = 0;
for(int j=i+1; j<n; j++){
if(str[i]>str[j])
count++;
}
result += count*factory[n-i-1];
}
if(!vis[result]){
vis[result] = 1;//标记为已经出现过
return 1;
}
else
return 0;
}
int bfs(){
node head;
queue<node> q;
memcpy(head.state,start,sizeof(head.state));
head.count = 0;
Cantor(head.state,9);
q.push(head);
while(!q.empty()){
head = q.front();
q.pop();
int z;
for(z = 0; z<9; z++)
if(head.state[z] == 0)//记录0的位置
break;
int x,y;
x = z%3;
y = z/3;//转化为二维坐标
for(int i = 0; i<4; i++){
//4个方向
int newx,newy;
newx = x + dir[i][0];
newy = y + dir[i][1];
int nz = newx + 3*newy;//转化回一维坐标
if(newx>=0 && newx<3 && newy>=0 && newy <3){
//没有越界
node newnode;
memcpy(&newnode,&head,sizeof(node));
swap(newnode.state[z],newnode.state[nz]);//换位
if(i == 0){
newnode.d[newnode.count] = 'u';newnode.count++; }//记录每一步
if(i == 1){
newnode.d[newnode.count] = 'r';newnode.count++; }
if(i == 2){
newnode.d[newnode.count] = 'd';newnode.count++; }
if(i == 3){
newnode.d[newnode.count] = 'l';newnode.count++; }
if(memcmp(newnode.state,goal,sizeof(goal)) == 0){
//找到了
for(int j = 0; j<newnode.count; j++){
printf("%c",newnode.d[j]);
}
return 1;
}
if(Cantor(newnode.state,9)){
//不重复
q.push(newnode);
}
}
}
}
return -1;//没有找到
}
int main()
{
char s[100];
int k = 0;
gets(s);
char *p;
for( p = s; *p != '\0'; p++){
if( *p != ' '){
if(*p == 'x')
start[k++] = 0;//把x转化为0
else
start[k++] = *p -'0';
}
}
int num = bfs();
if(num == -1)
cout<<"unsolvable"<<endl;
cin.get();
cin.get();
return 0;
}
Just started to learn bfs, record it, if there is any problem, I hope you can point it out.