八数码问题（刘汝佳版）

Posted 2021-01-21 kasenbob

可以采用dfs，对空白点进行操作，然后可用编码法，哈希表或者集合来标记，代码如下

#include<iostream>
#include<algorithm>
#include<cstring>
#include<string>
#include<set>
using namespace std;

typedef int State[9];
const int maxstate = 1000000;
State st[maxstate], goal;
int dist[mastate];
const int dx[] = { -1,1,0,0 };
const int dy[] = { 0,0,-1,1 };

//±à??·¨ 
int vis[362880], fact[9];
void init_lookup_table()
{
    fact[0] = 1;
    for (int i = 1; i<9; i++)
        fact[i] = fact[i - 1] * i;
}

int try_to_insert(int s)
{
    int code = 0;
    for (int i = 0; i<9; i++)
    {
        int cnt = 0;
        for (int j = i + 1; j<9; j++)
            if (st[s][j]<st[s][i])cnt++;
        code += act[8 - i] * cnt;
    }
    if (vis[code])return 0;
    return vis[code] = 1;
}

//1t?￡±í·¨ 
const int hashsize = 1000003;
int head[hashsize], next[hashsize];
void init_lookup_table()
{
    memset(head, 0, sizeof(head));
}
int hash(State& s)
{
    int v = 0;
    for (int i = 0; i<9; i++)
        v = v * 10 + s[i];
    return v % hashsize;
}
int try_to_insert(int s)
{
    int h = hash(st[s]);
    int u = head(h);
    while (u)
    {
        if (memcmp(st[u], st[s],sizeof(st[s]))==0)
            return 0;
        u=next[u];
    }
    next[s]=head[u];
    head[h]=s;
    return 1;
}

//STL?ˉo?
set<int>vis;
void init_lookup_table()
{
    vis.clear();
}
int try_to_insert(int s)
{
    int v=0;
    for(int i=0;i<9;i++)
    {
        v=v*10+st[s][i];
    }
    i(vis.count(v))
        return 0;
    vis.insert(v);
    return 1;
}

int bfs()
{
    init_lookup_table();
    int front = 1, rear = 2;
    while (front<rear)
    {
        State& s = st[front];
        if (memcmp(goal, s, sizeo(s)) == 0)return front;
        int z;
        for (int z = 0; z<9; z++)
        {
            if (!s[z])
                break;
        }
        int x = z / 3, y % 3;
        for (int d = 0; d<4; d++)
        {
            int newx = x + dx[d];
            int newy = y + dy[d];
            int newz = newx * 3 + newy;
            if (newx >= 0 && newx<3 && newy >= 0 && newy<3)
            {
                State& t = st[rear];
                memcpy(&t, &s, sizeof(s));
                t[newz] = s[z];
                t[z] = s[newz];
                dist[rear] = dist[front] + 1;
                if (try_to_insert(rear))rear++;
            }
        }
        front++;
    }
    return 0;
}

int main()
{
    for (int i = 0; i<9; i++)
        scanf("%d", &st[1][i]);
    for (int i = 0; i<9; i++)
        scanf("%d", &goal[i]);
    int ans = bfs();
    ans>0 ? printf("%d
", dist[ans]) : printf("-1
");
    return 0;
}