机器人的运动范围

链接：https://www.nowcoder.com/questionTerminal/6e5207314b5241fb83f2329e89fdecc8?f=discussion
来源：牛客网

public class Solution {

    public int movingCount(int threshold, int rows, int cols) {
        int flag[][] = new int[rows][cols]; //记录是否已经走过
        return helper(0, 0, rows, cols, flag, threshold);
    }

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

    private int numSum(int i) {
        int sum = 0;
        do{
            sum += i%10;
        }while((i = i/10) > 0);
        return sum;
    }
}