PROG-1149: บีคุนบันคุง (2Bk)

#include <bits/stdc++.h>

using namespace std;
using pii = pair<int,pair<int,int> >;
int n;
int land[1005][1005];
priority_queue<pii,vector<pii>,greater<pii> > Q;
int dx[4] = {0,0,1,-1};
int dy[4] = {1,-1,0,0};
bool visited[1005][1005];

bool checkpos(int x,int y){
    return x>=1 and x<=n and y>=1 and y<=n;
}

int main(){
    scanf("%d",&n);
    int x,y;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            scanf("%d",&land[i][j]);
            if(land[i][j] == 0 and !start){
                x = i;
                y = j;
                break;
            }
        }
    }
    Q.push({-1,{x,y}});
    int weight_max = -1;
    while(!Q.empty()){
        x = Q.top().second.first;
        y = Q.top().second.second;
        int w = Q.top().first;
        Q.pop();
        if(w==0){
            printf("%d",weight_max);
            break;
        }
        visited[x][y] = true;
        weight_max = max(w,weight_max);
        for(int i=0;i<4;i++){
            int k = x+dx[i];
            int j = y+dy[i];
            if(checkpos(k,j) and !visited[k][j]){
                Q.push({land[k][j],{k,j}});
            }
        }
    }
}