求助

#include<bits/stdc++.h>
using namespace std;
struct node
{
    int x,y,step;
    node(int xx,int yy,int tep)
    {
        x=xx;
        y=yy;
        step=tep;
    }
};
int dx[10]={0,1,0,-1},dy[10]={1,0,-1,0},v[305][305],m,vis[305][305],ans=0x7fffffff;
queue<node> q;
inline void bfs()
{
    while(!q.empty())q.pop();
    q.push(node(0,0,0));
    vis[0][0]=1;
    while(!q.empty())
    {
        node now=q.front();
        q.pop();
        int x=now.x,y=now.y;
        if(!v[x][y])
        {
            ans=min(ans,now.step);
        }
        for(int i=0;i<4;i++)
        {
            int tx=x+dx[i],ty=y+dy[i];
            if(tx<0||ty<0||tx>=300||ty>=300)continue;
            if(vis[tx][ty]||v[tx][ty]<=now.step)continue;
            vis[tx][ty]=1;
            q.push(node(tx,ty,now.step+1));
        }
    }
}
int main()
{
    cin>>m;
    for(int i=1;i<=m;i++)
    {
        int u,V,w;
        cin>>u>>V>>w;
        v[u][V]=w;
        if(u-1>=0)
        if(!v[u-1][V])
        v[u-1][V]=w;
        else v[u-1][V]=min(v[u-1][V],w);
        v[u+1][V]=w;
        if(V-1>=0)
        if(!v[u][V-1])
        v[u][V-1]=w;
        else
        v[u][V-1]=min(v[u][V-1],w);
        if(!v[u][V+1])
        v[u][V+1]=w;
        else
        v[u][V+1]=min(v[u][V+1],w);
    }
    bfs();
    cout<<ans<<"\n";
}