机器人的运动范围

public class Solution {
    public int movingCount(int threshold, int rows, int cols)
    {
        int visited[][] = new int[rows][cols];
        return helper(threshold, rows, cols, 0, 0, visited);
    }
    public int helper(int threshold, int rows, int cols, int i, int j, int[][] visited) {
        if(i<0||i>=rows||j<0||j>=cols||visited[i][j]==1||(bitSum(i)+bitSum(j))>threshold)
            return 0;
        visited[i][j] = 1;
        return helper(threshold, rows, cols, i+1, j, visited)
            + helper(threshold, rows, cols, i-1, j, visited)
            + helper(threshold, rows, cols, i, j+1, visited)
            + helper(threshold, rows, cols, i, j-1, visited)+1;
    }
    public int bitSum(int t) {
        int count = 0;
        do{
            count += t % 10;
            t = t/10;
        }while(t > 0);
        return count;
    }
}