Fire in the cell

#include <queue> 
bool corner(int x  , int y, int n , int m)
{
    return (x == 0 && y== 0) || (x == 0 && y == m - 1) || (y == 0 && x ==n - 1) || (x == n - 1 && y == m - 1) ; 
}
int fireInTheCells(vector<vector<int>> &mat, int n, int m, int s, int t) {
    // Write your code here.
    queue < pair <int, pair <int, int >> > q ; 
    for(int i = 0 ; i < n ; i++)
    {
        for(int j = 0 ; j < m ; j++)
        {
            if(mat[i][j] == 0)
            {
              q.push({0 , {i, j}});
            }
        }
    }
    vector < vector <int> > time(n ,vector <int> (m ,0))  ;   ; 
    vector <vector <int> > vis(n ,vector <int> (m ,0))  ; 
    while(!q.empty())
    {
        pair <int, pair <int, int >> f = q.front() ;
        int curtime =   f.first ; 
        int x = f.second.first ;
        int y = f.second.second ;
        vis[x][y] = 1; 
        time[x][y] = curtime ;
        int xcor[4] = {1, 0 , -1,0};
        int ycor[4] = {0 , 1, 0 , -1} ;
        q.pop() ;
        for(int i = 0 ; i < 4 ; i++)
        {
            int a = x + xcor[i] ;
            int b = y + ycor[i] ;
            if(a >= 0 && b >=0 && a < n && b < m && vis[a][b] == 0)
            {
                q.push({ curtime + 1,{a,b}}) ;
                vis[a][b] = 1;
            }

        }
    } 
    queue < pair <int, pair <int, int >>> check ;
    check.push({0 ,{s, t}});
    while(!check.empty())
    {
       pair <int, pair <int, int >> f = check.front() ;
       int curtime =   f.first ; 
        int x = f.second.first ;
        int y = f.second.second ;
        if((x == 0 || x == n - 1 || y == 0  || y == m - 1 ) && !corner(x,y ,n , m))
        {
            return curtime ; 
        }
        int xcor[4] = {1, 0 , -1,0};
        int ycor[4] = {0 , 1, 0 , -1} ;
        check.pop() ;
        for(int i = 0 ; i < 4 ; i++)
        {
            int a = x + xcor[i] ;
            int b = y + ycor[i] ;
            if(a >= 0 && b >=0 && a < n && b < m && curtime + 1  < time[a][b])
            {
                check.push({curtime + 1,{a,b}}) ;
               
            }

        }

    }
    return -1; 
}