求助P14273

#include<bits/stdc++.h>
using namespace std;
const int maxn=2e3;
int n,m,ans=0,indeg[maxn+5][maxn+5];
char a[maxn+5][maxn+5]; 
struct Edge{int to_x,to_y,next;}edge[4*maxn*maxn+5];//RE
int head[maxn+5][maxn+5],cnt=0;
queue< pair<int,int> > q;
void add(int from_x,int from_y,int to_x,int to_y) {
    edge[cnt].to_x=to_x;
    edge[cnt].to_y=to_y;
    edge[cnt].next=head[from_x][from_y];
    head[from_x][from_y]=cnt++;
}
void solve(int x,int y){
    if(a[x][y]=='.') return;
    int xx=0,yy=0;
    if(a[x][y]=='N') xx=-1;
    else if(a[x][y]=='S') xx=1;
    else if(a[x][y]=='E') yy=1;
    else if(a[x][y]=='W') yy=-1;
    int nx=x+xx,ny=y+yy;
    while(nx>=1&&ny>=1&&nx<=n&&ny<=m){
        if(a[nx][ny]!='.'){
            add(nx,ny,x,y);
            indeg[x][y]++;
        }
        nx+=xx;
        ny+=yy;
    }
}
int main(){
    memset(head,-1,sizeof(head));
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;++i)
        for(int j=1;j<=m;++j) cin>>a[i][j];
    for(int i=1;i<=n;++i)
        for(int j=1;j<=m;++j) solve(i,j);
    for(int i=1;i<=n;++i)
        for(int j=1;j<=m;++j)
            if(a[i][j]!='.'&&indeg[i][j]==0){
                q.push(make_pair(i,j));
                a[i][j]='.';
            }
    while(!q.empty()){
        int x=q.front().first,y=q.front().second;
        q.pop();
        ans++;
        for(int i=head[x][y];i!=-1;i=edge[i].next){
            int xx=edge[i].to_x,yy=edge[i].to_y;
            indeg[xx][yy]--;
            if(a[xx][yy]!='.'&&indeg[xx][yy]==0){
                q.push(make_pair(xx,yy));
                a[xx][yy]='.';
            }
        }
    }
    cout<<ans;
    return 0;
}