USACO msquare

　　使用康拓展开判重就行， 代码如下：

/*
    ID: m1500293
    LANG: C++
    PROG: msquare
*/

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <string>
#include <iostream>

using namespace std;
int target[8];


struct State
{
    int a[8];
    int len;
    string op;
    State() {}
    State(int b[], int l, string s)
    {
        for(int i=0; i<8; i++) a[i] = b[i];
        len = l;
        op = s;
    }
}res;


void opA(int a[])
{
    swap(a[0], a[7]);
    swap(a[1], a[6]);
    swap(a[2], a[5]);
    swap(a[3], a[4]);
}
void opB(int a[])
{
    int tp = a[3];
    for(int i=3; i>=1; i--) a[i]=a[i-1];
    a[0] = tp;
    tp = a[4];
    for(int i=4; i<=6; i++) a[i]=a[i+1];
    a[7] = tp;
}
void opC(int a[])
{
    int tp = a[1];
    a[1] = a[6];
    a[6] = a[5];
    a[5] = a[2];
    a[2] = tp;
}

int getnum(int a[])
{
    int res = 0;
    int fac[9];
    fac[0] = 1;
    for(int i=1; i<9; i++)  fac[i] = i*fac[i-1];
    for(int i=0; i<8; i++)
    {
        int cnt = 0;
        for(int j=0; j<i; j++) if(a[j]>a[i]) cnt++;
        res += cnt*fac[i];
    }
    return res;
}

bool vis[41000];
void bfs()
{
    memset(vis, 0, sizeof(vis));
    queue<State> que;
    int a[] = {1, 2, 3 ,4 ,5, 6, 7, 8};
    vis[getnum(a)] = 1;
    que.push(State(a, 0, ""));
    while(!que.empty())
    {
        State a = que.front(); que.pop();
        if(memcmp(a.a, target, sizeof(target)) == 0)
        {
            res = a;
            return ;
        }
        int tp[8];
        memcpy(tp, a.a, sizeof(tp));
        opA(tp);
        if(!vis[getnum(tp)])
        {
            vis[getnum(tp)] = 1;
            que.push(State(tp, a.len+1, a.op+"A"));
        }
        memcpy(tp, a.a, sizeof(tp));
        opB(tp);
        if(!vis[getnum(tp)])
        {
            vis[getnum(tp)] = 1;
            que.push(State(tp, a.len+1, a.op+"B"));
        }
        memcpy(tp, a.a, sizeof(tp));
        opC(tp);
        if(!vis[getnum(tp)])
        {
            vis[getnum(tp)] = 1;
            que.push(State(tp, a.len+1, a.op+"C"));
        }
    }
}

int main()
{
    freopen("msquare.in", "r", stdin);
    freopen("msquare.out", "w", stdout);
    for(int i=0; i<8; i++)
        scanf("%d", &target[i]);
    bfs();
    printf("%d\n", res.len);
    int output = 0;
    for(int i=0; i<res.len; i++)
    {
        cout<<res.op[i];
        output++;
        if(output == 60)
            cout<<endl;
    }
    if(res.len%60 != 0 || res.len==0)
        cout<<endl;
    return 0;
}