[leetCode]剑指 Offer 13. 机器人的运动范围

回溯法

机器人从(0,0)开始运动，进入坐标（i,j）时判断能否进入，如果能进入，再判断能否进入四个相邻的格子。

class Solution {
    public int movingCount(int m, int n, int k) {
        if(k < 0 || m <=0 || n <=0)
            return 0;
        boolean[][] visited = new boolean[m][n];
        return movingCountCore(visited,m,n,0,0,k);
    }

    private int movingCountCore(boolean[][] visited,
                                int rows, int cols,
                                int row, int col,int k){
        int count = 0;
        if(check(visited,rows, cols, row, col, k)){
            visited[row][col] = true;
            //只需向下或向右移动
            count = 1 + movingCountCore(visited, rows,cols,row + 1, col, k) //下
                      + movingCountCore(visited, rows,cols,row, col + 1, k);//右
        }
        return count;
    }

    private boolean check(boolean[][] visited,int rows, int cols ,int row, int col, int k){
        return row < rows && row >=0 && col < cols && col >= 0 && !visited[row][col] && digitSum(row) + digitSum(col) <= k;
    }

    private int digitSum(int number){
        int sum = 0;
        while(number > 0){
            sum+= number % 10;
            number /= 10;
        }
        return sum;
    }
}

广度优先搜索

class Solution {
    public int movingCount(int m, int n, int k) {
        if(k < 0 || m <=0 || n <=0)
            return 0;
        boolean[][] visited = new boolean[m][n];
        Queue<Pair<Integer,Integer>> queue = new LinkedList<>();
        queue.add(new Pair(0,0));
        int ans = 1;
        //定义两个方向：向右和向下
        int[] dx = {0,1};
        int[] dy = {1,0};
        while(!queue.isEmpty()){
            Pair<Integer,Integer> xy = queue.poll();
            int x = xy.getKey();
            int y = xy.getValue();
            for(int i = 0; i < 2; i++){//i = 0:向右；i=1：向下
                int tx = dx[i] + x;
                int ty = dy[i] + y;
                if(!check(visited, m, n, tx, ty, k)) continue;
                queue.add(new Pair<Integer,Integer>(tx, ty));
                visited[tx][ty] = true;
                ++ans;
            }
        }
        return ans;
    }

    private boolean check(boolean[][] visited,int rows, int cols ,int row, int col, int k){
        return row < rows && row >=0 && col < cols && col >= 0 && !visited[row][col] && digitSum(row) + digitSum(col) <= k;
    }

    private int digitSum(int number){
        int sum = 0;
        while(number > 0){
            sum+= number % 10;
            number /= 10;
        }
        return sum;
    }
}