Snake and ladder

class Solution {
public:
     int snakesAndLadders(vector<vector<int>>& board) {
    int n = board.size();
    int steps = 0;
    queue<int> q;
    vector<vector<bool>> visited(n, vector<bool>(n, false));
    q.push(1);
    visited[n-1][0] = true;
    while (!q.empty()) {
        int sz = q.size();
        for (int i = 0; i < sz; i++) {
            int f = q.front();
            q.pop();
            if (f == n*n) return steps;
            for (int k = 1; k <= 6; k++) {
                int curr=k+f;
                if (curr > n*n) break;
                int r =  n - (curr - 1) / n  -1;
                int c = (r%2==n%2)?n-1-(curr-1)%n:(curr-1)%n;
                if (visited[r][c]) continue;
                visited[r][c] = true;
                if (board[r][c] == -1) {
                    q.push(curr);
                } else {
                    q.push(board[r][c]);
                }
            }
        }
        steps++;
    }
    return -1;
}
};