「eight」Eight - seo实验室

eight

The 15-puzzle has been around for over 100 years; even if you don't know it by that name, you've seen it. It is constructed with 15 sliding tiles, each with a number from 1 to 15 on it, and all packed into a 4 by 4 frame with one tile missing. Let's call the missing tile 'x'; the object of the puzzle is to arrange the tiles so that they are ordered as:

 1  2  3  4
 5  6  7  8
 9 10 11 12
13 14 15  x

where the only legal operation is to exchange 'x' with one of the tiles with which it shares an edge. As an example, the following sequence of moves solves a slightly scrambled puzzle:

 1  2  3  4     1  2  3  4     1  2  3  4     1  2  3  4
 5  6  7  8     5  6  7  8     5  6  7  8     5  6  7  8
 9  x 10 12     9 10  x 12     9 10 11 12     9 10 11 12
13 14 11 15    13 14 11 15    13 14  x 15    13 14 15  x
            r->            d->            r->

The letters in the previous row indicate which neighbor of the 'x' tile is swAPPed with the 'x' tile at each step; legal values are 'r','l','u' and 'd', for right, left, up, and down, respectively.

Not all puzzles can be solved; in 1870, a man named Sam Loyd was famous for distributing an unsolvable version of the puzzle, and

frustrating many people. In fact, all you have to do to make a regular puzzle into an unsolvable one is to swap two tiles (not counting the missing 'x' tile, of course).

In this problem, you will write a program for solving the less well-known 8-puzzle, composed of tiles on a three by three

arrangement.

Input

You will receive, several descriptions of configuration of the 8 puzzle. One description is just a list of the tiles in their initial positions, with the rows listed from top to bottom, and the tiles listed from left to right within a row, where the tiles are represented by numbers 1 to 8, plus 'x'. For example, this puzzle

1 2 3

x 4 6

7 5 8

is described by this list:

1 2 3 x 4 6 7 5 8

Output

You will print to standard output either the word ``unsolvable'', if the puzzle has no solution, or a string consisting entirely of the letters 'r', 'l', 'u' and 'd' that describes a series of moves that produce a solution. The string should include no spaces and start at the beginning of the line. Do not print a blank line between cases.

Sample Input

2  3  4  1  5  x  7  6  8

Sample Output

ullddrurdllurdruldr

这道题，我学艺不精，没能掌握那么多的知识，我把自己会写的拿出来了，错了很多次，看网上的博客也看了，自己的境界没有那么多，紫书上面200页也看了，还是没学会。最后把我的代码给大家，思路就是一个广搜，重点是把这些操作步骤放在string里面，最后的时候输出。咋说呢，这道题肯定还会做的，等我学完搜索，我会补上它。今天发现这里的内存超限一定要控制他的数组开的范围，不要太大，不然你会坑惨了，呜呜呜，我就是一个例子。

#include<stdio.h>

#include<string.h>

#include<queue>

#include<math.h>

#include<string>

#include<map>

#include<algorithm>

using namespace std;

int step[4][2]={0,1,0,-1,1,0,-1,0};

struct node

{

string a;

int s[3][3];

int x,y;

};

map<int,int>u;

map<int,string>v;

void bfs()

{

queue<node>Q;

node st,en;

int i,j,k=1;

for(i=0;i<3;i++)

for(j=0;j<3;j++)

st.s[i][j]=i*3+j+1;

st.s[2][2]=0;

st.x=2;

st.y=2;

Q.push(st);

u[123456780]=1;

while(!Q.empty())

{

st=Q.front();

Q.pop();

for(i=0;i<4;i++)

{

en.x=st.x+step[i][0];

en.y=st.y+step[i][1];

if(en.x<0||en.x>=3||en.y<0||en.y>=3)

continue;

for(j=0;j<3;j++)

for(k=0;k<3;k++)

en.s[j][k]=st.s[j][k];

swap(en.s[st.x][st.y],en.s[en.x][en.y]);

int sum=1;

for(j=0;j<3;j++)

for(k=0;k<3;k++)

sum=sum*10+en.s[j][k];

if(u[sum]==1)

continue;

u[sum]=1;

if(i==0)

en.a=st.a+'l';

else if(i==1)

en.a=st.a+'r';

else if(i==2)

en.a=st.a+'u';

else if(i==3)

en.a=st.a+'d';

Q.push(en);

v[sum]=en.a;

}

int main()

{

bfs();

char s[500010];

while(gets(s))

{

int l=strlen(s);

int i,sum=1;

for(i=0;i<l;i++)

{

if(s[i]>='1'&&s[i]<='9')

sum=sum*10+s[i]-'0';

else if(s[i]=='x')

sum*=10;

}

if(u[sum]==0)

printf("unsolvable\n");

else

{

string st=v[sum];

for(i=st.length()-1;i>=0;i--)

printf("%c",st[i]);

printf("\n");

}

return 0;

}

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