POJ 3131 Cubic Eight-Puzzle 雙向BFS + HASH

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超贊的一道搜尋題，麻煩到沒朋友，不過思路還是很清楚的。

雙向搜尋的時候需要注意一個地方就是起始狀態只有一個，目標狀態最多的時候感覺會有512個，所以要控制兩個方向搜尋的層數。第一次知道雙向搜尋還能控制層數，簡直點贊。

#include <algorithm>#include <iostream>#include <cstring>#include <cstdlib>#include <cstdio>#include <queue>#include <cmath>#include <stack>#include <map>#pragma comment(linker, "/STACK:1024000000");#define EPS (1e-8)#define LL long long#define ULL unsigned long long#define _LL __int64#define _INF 0x3f3f3f3f#define Mod 6000007using namespace std;char Map[5][5];int Judge(char a,char b,char c){    if(a == 'W')    {        if(b == 'R')            return 0;        return 5;    }    else if(a == 'R')    {        if(b == 'W')            return 1;        return 3;    }    else if(a == 'B')    {        if(b == 'R')            return 2;        return 4;    }    else return 6;}struct Q{    int sta,x,y,fl,ans;};int mark[3000010][2];int jx[] = { 0, 0, 1,-1};int jy[] = {-1, 1, 0, 0};int re[10][10];int bit[10];struct H{    int site,data,next;}st[Mod];int head[Mod];int Top_H;int Query(int data,int Top){    int temp = data%Mod;    int p = head[temp];    for(;p != -1; p = st[p].next)    {        if(st[p].data == data)            return st[p].site;    }    p = Top_H++;    st[p].data = data;    st[p].site = Top;    st[p].next = head[temp];    head[temp] = p;    return -1;}int bfs(int x,int y){    Top_H = 0;    memset(mark,-1,sizeof(mark));    int Top = 0;    int i,j;    for(i = 0;i < Mod; ++i)        head[i] = -1;    int sta = 0;    for(i = 0; i < 3; ++i)    {        for(j = 0; j < 3; ++j)            if(i == x && j == y)                sta += Judge('E','E','E')*bit[i*3+j+1];            else                sta += Judge('W','B','R')*bit[i*3+j+1];    }    Q f,t;    queue<Q> q;    f.sta = sta;    f.ans = 0,f.x = x,f.y = y,f.fl = 0;    q.push(f);    Query(f.sta,Top);    mark[Top][0] = 0;    Top++;    f.ans = 0;    f.fl = 1;    for(i = 0; i < 512; ++i)    {        sta = 0,x = 0,y = 0;        for(j = 0; j < 9; ++j)        {            if(Map[x][y] == 'E')            {                f.x = x;                f.y = y;                sta += Judge('E','E','E')*bit[x*3+y+1];            }            else if(i&(1<<j))            {                if(Map[x][y] == 'W')                    sta += Judge('W','R','B')*bit[x*3+y+1];                else if(Map[x][y] == 'R')                    sta += Judge('R','B','W')*bit[x*3+y+1];                else                    sta += Judge('B','R','W')*bit[x*3+y+1];            }            else            {                if(Map[x][y] == 'W')                    sta += Judge('W','B','R')*bit[x*3+y+1];                else if(Map[x][y] == 'R')                    sta += Judge('R','W','B')*bit[x*3+y+1];                else                    sta += Judge('B','W','R')*bit[x*3+y+1];            }            y++;            if(y == 3)                y = 0,x++;        }        f.sta = sta;        q.push(f);        if(Query(f.sta,Top) == -1)        {            mark[Top++][1] = 0;        }        else        {            mark[Query(f.sta,Top)][1] = 0;        }    }    int site,tsite,tdata;    while(q.empty() == false)    {        f = q.front();        q.pop();        if((f.fl == 1 && f.ans > 9) || (f.fl == 0 && f.ans > 20))            continue;        if(mark[Query(f.sta,Top)][f.fl^1] != -1)        {            return mark[Query(f.sta,Top)][f.fl^1] + f.ans;        }        site = f.x*3 + f.y;        t.fl = f.fl;        t.ans = f.ans+1;        for(i = 0; i < 4; ++i)        {            t.x = f.x + jx[i];            t.y = f.y + jy[i];            if(0 <= t.x && t.x <= 2 && 0 <= t.y && t.y <= 2)            {                tsite = t.x*3+t.y;                tdata = f.sta/bit[tsite+1]%7;                t.sta = f.sta/bit[tsite]*bit[tsite] + 6*bit[tsite+1] + f.sta%bit[tsite+1];                t.sta = t.sta/bit[site]*bit[site] + re[tdata][i]*bit[site+1] + t.sta%bit[site+1];                if(Query(t.sta,Top) == -1)                {                    mark[Top++][t.fl] = t.ans;                    q.push(t);                }                else if(mark[Query(t.sta,Top)][t.fl] == -1)                {                    mark[Query(t.sta,Top)][t.fl] = t.ans;                    q.push(t);                }            }        }    }    return -1;}int main(){    re[0][0] = 1;    re[0][1] = 1;    re[0][2] = 2;    re[0][3] = 2;    re[1][0] = 0;    re[1][1] = 0;    re[1][2] = 4;    re[1][3] = 4;    re[2][0] = 3;    re[2][1] = 3;    re[2][2] = 0;    re[2][3] = 0;    re[3][0] = 2;    re[3][1] = 2;    re[3][2] = 5;    re[3][3] = 5;    re[4][0] = 5;    re[4][1] = 5;    re[4][2] = 1;    re[4][3] = 1;    re[5][0] = 4;    re[5][1] = 4;    re[5][2] = 3;    re[5][3] = 3;    int i,j,x,y;    bit[9] = 1;    for(i = 8; i >= 0; --i)        bit[i] = bit[i+1]*7;    while(scanf("%d %d",&y,&x) && (x||y))    {        for(i = 0; i < 3; ++i)        {            for(j = 0; j < 3; ++j)            {                scanf("%*c%c",&Map[i][j]);            }        }        printf("%d\n",bfs(x-1,y-1));    }    return 0;}