三明治

题目描述

做法

对于每个格子(i,j)设L(i,j)表示先吃靠左边界的格子至少要吃多少格子，R意义类似。
然后你发现L(i,j)>=L(i,j-1)。
于是一行一行做，每行才清空一次标记数组。

#include <cstdio>
#include <algorithm>
#define fo(i,a,b) for(i=a;i<=b;i++)
#define fd(i,a,b) for(i=a;i>=b;i--)
using namespace std;
const int maxn=400+10,inf=1000000005;
const int fx[4][2]={{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
const int trans[2][4]={{3, 2, 1, 0}, {2, 3, 0, 1}};
char s[maxn][maxn];
int L[maxn][maxn],R[maxn][maxn],bz[maxn][maxn];
int i,j,k,l,t,n,m,ans;
char get(){
    char ch=getchar();
    while (ch!='Z'&&ch!='N') ch=getchar();
    return ch;
}
int dfs(int x,int y,int f){
    if (bz[x][y]==1) return inf;
    if (bz[x][y]==2) return 0;
    bz[x][y]=1;
    int i,d[2];
    d[0]=f;d[1]=trans[s[x][y]=='Z'][f];
    int ans=2,xx,yy;
    fo(i,0,1){
        xx=x+fx[d[i]][0];yy=y+fx[d[i]][1];
        if (1<=xx&&xx<=n&&1<=yy&&yy<=m) ans+=dfs(xx,yy,d[i]);
    }
    bz[x][y]=2;
    return min(ans,inf);
}

int main() {
    freopen("sandwich.in","r",stdin);freopen("sandwich.out","w",stdout);
    scanf("%d%d", &n, &m);
    fo(i,1,n)
        fo(j,1,m)
            s[i][j]=get();
    fo(i,1,n){
        fo(j,1,n)
            fo(k,1,m)
                bz[j][k]=0;
        fo(j,1,m) L[i][j]=min(L[i][j-1]+dfs(i,j,2),inf);
    }
    fo(i,1,n){
        fo(j,1,n)
            fo(k,1,m)
                bz[j][k]=0;
        fd(j,m,1) R[i][j]=min(R[i][j+1]+dfs(i,j,3),inf);
    }
    fo(i,1,n){
        fo(j,1,m){
            ans=min(L[i][j],R[i][j]);
            if (ans!=inf) printf("%d ",ans); else printf("-1 ");
        }
        printf("\n");
    }
}