UVA 12510/CSU 1119 Collecting Coins DFS

前年的省赛题，难点在于这个石头的推移不太好处理

后来还是看了阳神当年的省赛总结，发现这个石头这里，因为就四五个子，就暴力dfs处理即可。先把石头当做普通障碍，进行一遍全图的dfs或者bfs，找到可以找的点，然后dfs每次探索新区域的新点即可，想通了这里很好做了

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
char mat[][];
int vis[][];
int rock[][],cnt;
int n,m;
int dir[][]={{,},{-,},{,},{,-}};
int inq[];
int res,sum;
void dfs1(int sx,int sy,int col)
{
    vis[sx][sy]=col;
    for (int i=;i<;i++){
        int nx=sx+dir[i][];
        int ny=sy+dir[i][];
        if (nx< || nx>=n || ny< || ny>=m) continue;
        if (vis[nx][ny]) continue;
        if (mat[nx][ny]=='O'|| mat[nx][ny]=='X') continue;

        if(mat[nx][ny]=='C'){
           res++;
        }
        dfs1(nx,ny,col);
    }
}
void back(int x,int y,int col)
{
    vis[x][y]=;
    for (int i=;i<;i++){
        int nx=x+dir[i][];
        int ny=y+dir[i][];
        if (nx< || ny< || nx>=n || ny>=m) continue;
        if (vis[nx][ny]!=col) continue;
        back(nx,ny,col);
    }

}
int maxn,ans;
void proc(int num)
{
    char cc;
    if (num>=cnt) return;
    for (int i=;i<cnt;i++){
        if (inq[i]) continue;
        inq[i]=;
        int x=rock[i][];
        int y=rock[i][];
        for (int j=;j<;j++){
            int dx=x+dir[j][];
            int dy=y+dir[j][];
            if (dx< || dx>=n || dy< || dy>=m) continue;
            if (mat[dx][dy]=='X') continue;
            if (!vis[dx][dy]) continue;
            int tx=x-dir[j][];
            int ty=y-dir[j][];
            if (tx< || tx>=n || ty< || ty>=m) continue;
            if (mat[tx][ty]!='.' && !vis[tx][ty]) continue;
            cc=mat[tx][ty];
            mat[tx][ty]='O';
            mat[x][y]='.';
            res=;
            dfs1(x,y,i+);
            maxn+=res;
            int tmp=res;
            ans=max(ans,maxn);
            proc(num+);
            back(x,y,i+);
            maxn-=tmp;
            mat[tx][ty]=cc;
            mat[x][y]='O';
        }
        proc(num+);
        inq[i]=;
    }

}
int main()
{
    int t,sx,sy;
    scanf("%d",&t);
    while (t--)
    {
        cnt=;
        scanf("%d%d",&n,&m);
        for (int i=;i<n;i++){
            scanf("%s",mat[i]);
            for (int j=;j<m;j++){
                vis[i][j]=;
                if (mat[i][j]=='S'){
                    sx=i;sy=j;mat[i][j]='.';
                }
                else
                if (mat[i][j]=='O'){
                    rock[cnt][]=i;
                    rock[cnt++][]=j;
                }
            }
        }
        res=;
        dfs1(sx,sy,);
        sum=res;
        maxn=,ans=;
        memset(inq,,sizeof inq);
        proc();
        ans+=sum;
        printf("%d\n",ans);
    }
    return ;
}