状态压缩BFS

魔板，状态压缩BFS

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<unordered_map>
#include<queue>
#include<utility>
using namespace std;

unordered_map<string, int> dist; //记录变换到当前状态所需要的步骤数
unordered_map<string, pair<char, string> > pre_s; //记录当前状态的上一个状态时什么，以及如何变化而来的
queue<string> q;
string st, en;
//开始时的序列和目标序列
int g[2][4];

string pull()
{
   
    //数组转字符串
    string res;
    for (int i = 0; i < 4; i++) {
   
        res.append(1, char(g[0][i]));
    }
    for (int i = 3;i >=0; i--) {
   
        res.append(1, char(g[1][i]));
    }

    return res;
}

void push(string t)
{
   
    //字符串转数组
    for (int i = 0; i < 4; i++) {
   
        g[0][i] = t[i];
    }
    for (int i = 3; i >=0; i--) {
   
        g[1][i] = t[7 - i];
    }
}

string move_a(string t)
{
   
    //交换上下两行
    push(t);
    for (int i = 0; i < 4; i++) {
   
        swap(g[0][i], g[1][i]);
    }

    return pull();
}
string move_b(string t)
{
   
    push(t);
    int tmp[2] = {
   g[0][3], g[1][3]};
    for (int i = 3; i > 0; i--) {
   
        g[0][i] = g[0][i - 1];
        g[1][i] = g[1][i - 1]; 
    }
    g[0][0] = tmp[0];
    g[1][0] = tmp[1];

    return pull();
}
string move_c(string t)
{
   
    push(t);
    int tmp = g[0][1];
    g[0][1] = g[1][1];
    g[1][1] = g[1][2];
    g[1][2] = g[0][2];
    g[0][2] = tmp;
    
    return pull();
}

void bfs() 
{
   
    dist[st] = 0;
    q.push(st);
    char mov[] = {
   'A', 'B', 'C'};
    while (!q.empty())
    {
   
        string t = q.front();
        int d = dist[t];
        q.pop();
        string m[3];
        m[0] = move_a(t);
        m[1] = move_b(t);
        m[2] = move_c(t);
        for (int i = 0; i < 3; i++) {
   
            if (dist.count(m[i]) == 0) {
   
                dist[m[i]] = d + 1;
                pre_s[m[i]] = make_pair(mov[i], t);
                if (m[i] == en){
   
                    return;
                }
                q.push(m[i]);
            }
        }
    }
}

int main() 
{
   
#ifndef ONLINE_JUDGE
    freopen("D:/VS CODE/C++/in.txt", "r", stdin);
    freopen("D:/VS CODE/C++/out.txt", "w", stdout);
#endif
    for (int i = 0; i < 2; ++i) {
   
        for (int j = 0; j < 4; ++j) {
   
            int a; cin >> a;
            en += char('0' + a);
        }
    }
    st = "12345678";

    if (st == en) {
   
        cout << 0;
        return 0;
    }
    
    bfs();

    int d = dist[en];
    cout << d << endl;
    string p = en;
    string ans;
    while (p != st) {
   
        ans.append(1, pre_s[p].first);
        p = pre_s[p].second;
    }
    reverse(ans.begin(), ans.end());
    cout << ans << endl;

    fclose(stdin);
    fclose(stdout);
    return 0;
}