t records the earliest time each grid was smashed, bfs(x, y, t) indicates that the current state is the (x, y) grid, and the time is t. Because of bfs, the t found first must be smaller than the one found later, so a grid can be searched once
#include<iostream>
#include<cstdio>
#include<queue>
using namespace std;
const int N=505,inf=1e9,dx[]={-1,1,0,0,0},dy[]={0,0,-1,1,0};
int n,m,t[N][N];
bool v[N][N];
struct qwe
{
int x,y,t;
qwe(int X=0,int Y=0,int T=0)
{
x=X,y=Y,t=T;
}
};
queue<qwe>q;
int read()
{
int r=0,f=1;
char p=getchar();
while(p>'9'||p<'0')
{
if(p=='-')
f=-1;
p=getchar();
}
while(p>='0'&&p<='9')
{
r=r*10+p-48;
p=getchar();
}
return r*f;
}
inline bool ok(int x,int y,int z)
{
return x>=0&&y>=0&&t[x][y]>z&&!v[x][y];
}
int main()
{
n=read();
for(int i=0;i<=500;i++)
for(int j=0;j<=500;j++)
t[i][j]=inf;
for(int i=1;i<=n;i++)
{
int x=read(),y=read(),z=read();
for(int j=0;j<5;j++)
if(x+dx[j]>=0&&y+dy[j]>=0)
t[x+dx[j]][y+dy[j]]=min(t[x+dx[j]][y+dy[j]],z);
}
q.push(qwe(0,0,0));
v[0][0]=1;
while(!q.empty())
{
int x=q.front().x,y=q.front().y,z=q.front().t;
q.pop();
if(t[x][y]==inf)
{
printf("%d\n",z);
return 0;
}
for(int i=0;i<4;i++)
if(ok(x+dx[i],y+dy[i],z+1))
{
v[x+dx[i]][y+dy[i]]=1;
q.push(qwe(x+dx[i],y+dy[i],z+1));
}
}
puts("-1");
return 0;
}