机器人的运动范围

使用递归，判断所有的点机器人是否可达即可

public class Solution {
    public int movingCount(int threshold, int rows, int cols)
    {
        int[][] flag = new int[rows][cols];  /*记录已经走过的点*/
        return helper(0,0,rows,cols,flag,threshold);
    }

    public int helper(int i, int j, int rows, int cols, int[][] flag, int threshold){
        if(i < 0 || i >= rows || j < 0 || j >= cols || flag[i][j] == 1 || numSum(i)+numSum(j) > threshold)
            return 0;
        flag[i][j] = 1;
        return helper(i+1,j,rows,cols,flag,threshold)+helper(i-1,j,rows,cols,flag,threshold)+
            helper(i,j+1,rows,cols,flag,threshold)+helper(i,j-1,rows,cols,flag,threshold)+1;
    }

    // 计算坐标的数位和
    public int numSum(int num){
        int sum = 0;
        while(num > 0){
            sum += num%10;
            num /= 10;
        }
        return sum;
    }
}