MovingCount.java

package com.company;

import org.junit.Test;

public class MovingCount {
    public int movingCount(int threshold, int rows, int cols) {
        int count = 0;
        if (threshold < 1 || rows < 1 || cols < 1) {
            return count;
        }
        boolean[] visited = new boolean[rows * cols];
        count = movingCountCore(threshold, rows, cols, 0, 0, visited);
        return count;
    }

    public int movingCountCore(int threshold, int rows, int cols, int row, int col, boolean[] visited) {
        int count = 0;
        if (row >= 0 && row < rows && col >= 0 && col < cols &&
                getDigitSum(row) + getDigitSum(col) <= threshold &&
                !visited[row * cols + col]) {
            visited[row * cols + col] = true;
            count = 1 + movingCountCore(threshold, rows, cols, row + 1, col, visited)
                    + movingCountCore(threshold, rows, cols, row - 1, col, visited)
                    + movingCountCore(threshold, rows, cols, row, col + 1, visited)
                    + movingCountCore(threshold, rows, cols, row, col - 1, visited);
        }
        return count;
    }

    public int getDigitSum(int num) {
        int sum = 0;
        while (num != 0) {
            sum += num % 10;
            num /= 10;
        }
        return sum;
    }

    @Test
    public void test() {

    }
}