Check if There is a Valid Path in a Grid.cpp

class Solution {
public:
    
    bool hasValidPath(vector<vector<int>>& grid) 
    {
        int m = grid.size();
        int n = grid[0].size();
        if(m==1 and n==1) return true;
        // 2D - direction vector for all streets
        // 0th based indexing 0 to 11
        
        // Let grid value g[i][j] = 4, means we need to follow "street-4" direction
        // First index of street-4 direction = 2*(4-1) = 6
        // Second index of street-4 direction = 2*(4-1)+1 = 7
        // dir[6] = {0, 1}
        // dir[7] = {1, 0}
        vector<vector<int>>dir = {        // Indices   
            {0,-1}, {0, 1}, // street 1  -->  0  1
            {-1,0}, {1, 0}, // street 2  -->  2  3
            {0,-1}, {1, 0}, // street 3  -->  4  5
            {0, 1}, {1, 0}, // street 4  -->  6  7
            {0,-1}, {-1,0}, // street 5  -->  8  9 
            {0, 1}, {-1,0}  // street 6  -->  10  11
        };

        vector<vector<bool>>vis(m, vector<bool>(n, false));
        queue<pair<int,int>>q;
        
        q.push({0, 0});
        vis[0][0] = true;
        
        while (!q.empty()) 
        {
            auto cur = q.front(); q.pop();

            int r = cur.first;
            int c = cur.second;
            int val = grid[r][c] - 1; // grid values 1 to 6
            
            if(r==m-1 and c==n-1) return true;
            
            // 2 directions from every cell
            for(int k=0;k<2;k++) // k = 0, k = 1
            {
                int idx = 2*val+k;   // get index
                int nr = r + dir[idx][0];
                int nc = c + dir[idx][1];
                if (nr < 0 or nr >= m or nc < 0 or nc >= n or vis[nr][nc]==true) continue;
                
                //  for checking the back direction matches with current cell i.e forming path to next cell
                for(int x=0;x<2;x++)
                {
                    int i = 2*(grid[nr][nc]-1)+x;   // get index
                    if(r == nr+dir[i][0] and c == nc+dir[i][1]){
                        vis[nr][nc] = true;
                        q.push({nr, nc});
                    }       
                }
            }
        }
        return false;
    }
};