HDU1043 八数码(BFS + 打表)

#include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
#include <cmath>
#include <string>
#include <string.h>
#include <algorithm>
using namespace std;
#define LL __int64
#define eps 1e-8
#define INF 1e8
#define lson l , m , rt << 1
#define rson m + 1 , r , rt << 1 | 1
const int MOD = 2333333; 
const int maxn = 362880;
bool vis[maxn];
string ans[maxn];
int fac[]={1 , 1 , 2 , 6 , 24 , 120 , 720 , 5040 , 40320 , 362880};

int Cantor(string str)
{
    int ret = 0;
    int n = str.size();
    for(int i = 0 ; i < n ; i++) {
        int cnt = 0;
        for(int j = i ; j < n ; j++)
            if(str[j] < str[i])
                cnt++;
        ret += cnt * fac[n - i - 1];
    }
    return ret;
}
void move_Up(string &str , int pos)
{
    swap(str[pos] , str[pos - 3]);
}
void move_Down(string &str , int pos)
{
    swap(str[pos] , str[pos + 3]);
}
void move_Left(string &str , int pos)
{
    swap(str[pos] , str[pos - 1]);
}
void move_Right(string &str , int pos)
{
    swap(str[pos] , str[pos + 1]);
}
void BFS(string start)
{
    memset(vis , 0 , sizeof(vis));
    queue <string> que;
    que.push(start);
    int x = Cantor(start);
    vis[x] = 1;
    ans[x] = "";
    int pos;
    while(!que.empty()) {
        string u = que.front();
        que.pop();
        int i = Cantor(u);
        for(pos = 0 ; pos < 9 ; pos++)
            if(u[pos] == ‘x‘)
                break;

        if(pos > 2) {
            string tmp = u;
            move_Up(tmp , pos);
            int k = Cantor(tmp);
            if(!vis[k]) {
                vis[k] = 1;
                que.push(tmp);
                ans[k] = ans[i] + ‘u‘;
            }
        }
        if(pos < 6) {
            string tmp = u;
            move_Down(tmp , pos);
            int k = Cantor(tmp);
            if(!vis[k]) {
                vis[k] = 1;
                que.push(tmp);
                ans[k] = ans[i] + ‘d‘;
            }
        }
        if(pos % 3 != 0) {
            string tmp = u;
            move_Left(tmp , pos);
            int k = Cantor(tmp);
            if(!vis[k]) {
                vis[k] = 1;
                que.push(tmp);
                ans[k] = ans[i] + ‘l‘;
            }
        }
        if(pos % 3 != 2) {
            string tmp = u;
            move_Right(tmp , pos);
            int k = Cantor(tmp);
            if(!vis[k]) {
                vis[k] = 1;
                que.push(tmp);
                ans[k] = ans[i] + ‘r‘;
            }
        }    
    }
}
int main() 
{
    char ch[30];
    string start = "12345678x";
    BFS(start);
    while(gets(ch))
    {
        string str = "";
        for(int i = 0 ; ch[i] != ‘\0‘ ; i++) {
            if(ch[i] == ‘ ‘)
                continue;
            else
                str += ch[i];
        }
        int k = Cantor(str);
        if(vis[k]) {
            for(int i = ans[k].size() - 1 ; i >= 0 ; i--) {
                if(ans[k][i] == ‘u‘)
                    putchar(‘d‘);
                else if(ans[k][i] == ‘d‘)
                    putchar(‘u‘);
                else if(ans[k][i] == ‘l‘)
                    putchar(‘r‘);
                else
                    putchar(‘l‘);
            }
            puts("");
        } else {
            cout << "unsolvable" << endl;
        }
    }
    return 0;
}