双向广搜20pts求条

#include<bits/stdc++.h>
using namespace std;
inline int read(){
    char c=getchar();
    int sum=0,flag=1;
    while(!isdigit(c)){if(c=='-')flag=-1;c=getchar();}
    while(isdigit(c)){sum=(sum<<1)+(sum<<3)+(c^48),c=getchar();}
    return sum*flag;
}
inline void write(int x){
    if(x<0) x=(~x)+1,putchar('-');
    if(x>9) write(x/10);
    putchar(x%10|48);
}
const int fx[4][2]={{0,1},{1,0},{0,-1},{-1,0}};
int n=read(),mp[1005][1005];
bool vis[1005][1005];
struct node{
    int x,y,cnt;
}s,t;
bool check(node a,node b){
    return abs(a.x-b.x)+abs(a.y-b.y)==1;
}//判断相遇
int bfs(node s,node t){
    queue<node>qf,qb;
    qf.push(s),qb.push(t);
    vis[s.x][s.y]=vis[t.x][t.y]=1;
    while(qf.size()&&qb.size()){
        node now;
        if(qf.size()<qb.size()){
            now=qf.front();qf.pop();
            for(int i=0;i<4;i++){
                int x=now.x+fx[i][0],y=now.y+fx[i][1];
                if(vis[x][y]||x>n||y>n||x<1||y<1||mp[x][y])
                    continue;
                qf.push((node){x,y,now.cnt+1});
                vis[x][y]=1;
                if(check(qf.back(),qb.back())) 
                    return qf.back().cnt+qb.back().cnt+1;
            }
        }
        else{
            now=qb.front();qb.pop();
            for(int i=0;i<4;i++){
                int x=now.x+fx[i][0],y=now.y+fx[i][1];
                if(vis[x][y]||x>n||y>n||x<1||y<1||mp[x][y])
                    continue;
                qb.push((node){x,y,now.cnt+1});
                vis[x][y]=1;
                if(check(qf.back(),qb.back())) 
                    return qf.back().cnt+qb.back().cnt+1;
            }       
        }
    }
    return -1;
}
int main(){
    for(int i=1;i<=n;i++){
        char c[1005];
        scanf("%s",c+1);
        for(int j=1;j<=n;j++){
            mp[i][j]=c[j]-'0';
        }
    }
    s.x=read(),s.y=read(),s.cnt=0;
    t.x=read(),t.y=read(),t.cnt=0;
    write(bfs(s,t));
    return 0;
}