http://blog.csdn.net/u013598409/article/details/43924465

相比于一年半前，代码的掌控能力强了许多。

#include <cstdio>
#include <algorithm>
#include <map>
using namespace std;

#define rep(i,a,b) for (int i=(a);i<=(b);i++)
#define per(i,a,b) for (int i=(a);i>=(b);i--)

const int dx[4]={0,0,-1,1};
const int dy[4]={-1,1,0,0};

char s[4][4];

int dep;
map<int,int> mp;

inline int cid(char c)
{
    if (c=='W') return 0;
    else if (c=='B') return 1;
    else if (c=='O') return 2;
}

inline int ST(void)
{
    int sum=0;
    rep(i,0,3)
        rep(j,0,3)
            sum=sum*3+cid(s[i][j]);
    return sum;
}

inline int Check(void)
{
    char t;
    rep(i,0,3)
    {
        t=s[i][0];
        if (t==s[i][1]&&t==s[i][2]&&t==s[i][3]) return 1;
    }

    rep(i,0,3)
    {
        t=s[0][i];
        if (t==s[1][i]&&t==s[2][i]&&t==s[3][i]) return 1;
    }

    t=s[0][0];
    if (t==s[1][1]&&t==s[2][2]&&t==s[3][3]) return 1;

    t=s[3][0];
    if (t==s[2][1]&&t==s[1][2]&&t==s[0][3]) return 1;

    return 0;
}

inline int Legal(int x,int y)
{
    return 0<=x&&x<=3&&0<=y&&y<=3;
}

int DFS(int dir,int tms,int lim)
{
    int st=ST();
    if (mp.count(st)) return 0;
    mp[st]=1;

    if (tms==lim)
    {
        int t=Check();
        return t;
    }

    rep(x,0,3) rep(y,0,3) if (cid(s[x][y])==dir)
        rep(k,0,3)
        {
            int nx=x+dx[k],ny=y+dy[k];
            if (Legal(nx,ny)&&cid(s[nx][ny])==2)
            {
                swap(s[x][y],s[nx][ny]);
                int t=DFS(dir^1,tms+1,lim);
                swap(s[x][y],s[nx][ny]);
                if (t) return 1;
            }
        }
    return 0;
}

int main(void)
{
//  freopen("codevs1004.in","r",stdin);
//  freopen("codevs1004.out","w",stdout);

    rep(i,0,3)
        scanf("%s",s[i]);

    int t1,t2; dep=-1;
    do
    {
        dep++;
        mp.clear();
        t1=DFS(0,0,dep);
        mp.clear();
        t2=DFS(1,0,dep);
    }while (!t1&&!t2);
    printf("%d\n",dep);

    return 0;
}