算法1

(回溯法) $O(n)$

判断当前位置是否满足条件，满足条件count+1，然后递归当前位置的下面的四个位置，以此类推，遍历整个地图即可。

java 代码

class Solution {
    public int movingCount(int threshold, int rows, int cols)
    {
        if(threshold<0||rows<0||cols<0)
            return 0;

        boolean[] visited = new boolean[rows*cols];
        for(int i = 0;i<rows*cols;i++){
            visited[i] = false;
        }
        int count = movintCountCore(threshold,rows,cols,0,0,visited);

        return count;
    }

    public int movintCountCore(int threshold,int rows,int cols,int row,int col,boolean[] visited){
        int count = 0;
        if(check(threshold,rows,cols,row,col,visited)){
            visited[row*cols+col] = true;

            count=1 + movintCountCore(threshold,rows,cols,row+1,col,visited)
                    + movintCountCore(threshold,rows,cols,row-1,col,visited)
                    + movintCountCore(threshold,rows,cols,row,col+1,visited)
                    + movintCountCore(threshold,rows,cols,row,col-1,visited);
        }

        return count;
    }

    boolean check(int threshold,int rows,int cols,int row,int col,boolean[] visited){
        if(row>=0&&col>=0&&row<rows&&col<cols
            &&getDigitSum(row)+getDigitSum(col)<=threshold
            &&!visited[row*cols+col])
            return true;

        return false;
    }

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

        return sum;
    }
}