八数码问题 经典搜索 bfs

/*这道题a的蛋疼无比啊。学了hash技术和cantor展开。具体的解释都在注释下。不多说了。好题啊！*/
#include<cstdio>
#include<set>
#include <cstring>
using namespace std;

typedef int State[9];
const int MAXSTATE = 1000000;
State st[MAXSTATE], goal;
int dist[MAXSTATE];

const int MAXHASHSIZE = 1000003;
int head[MAXHASHSIZE], next[MAXSTATE];
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 % MAXHASHSIZE;
}
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[h];
  head[h] = s;
  return 1;
}

const int dx[] = {-1, 1, 0, 0};
const int dy[] = {0, 0, -1, 1};
int bfs() {
  init_lookup_table();
  int front = 1, rear = 2;
  while(front < rear) {
    State& s = st[front];
    if(memcmp(goal, s, sizeof(s)) == 0) return front;
    int z;
    for(z = 0; z < 9; z++) if(!s[z]) break;
    int x = z/3, y = z%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() {
 int t;
    scanf("%d",&t);
    while(t--)
    {
        getchar();
        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();
        if(ans==0) printf("-1\n");
        else printf("%d\n",dist[ans]);
    }
  return 0;
}