[剑指offer] 机器人的运动范围

题目

https://www.acwing.com/problem/content/description/22/

思路

方法一

bfs。yxc大佬说如果数据大的时候c++写dfs可能会爆栈。

Java代码

import java.util.LinkedList;

class Solution {

    int[] dx = new int[]{-1, 0, 1, 0};
    int[] dy = new int[]{0, 1, 0, -1};

    public int movingCount(int threshold, int rows, int cols){
        if(rows == 0 || cols == 0) return 0;
        int res = 0;
        boolean[][] st = new boolean[rows][cols];
        LinkedList<int[]> q = new LinkedList<>();
        q.add(new int[]{0, 0});
        while(!q.isEmpty()){
            int[] t = q.pop();
            if(sum(t[0])+sum(t[1]) > threshold || st[t[0]][t[1]] == true)
                continue;
            
            res++;
            st[t[0]][t[1]] = true;
            for(int i=0; i<4; i++){
                int x = rows+dx[i], y = rows+dy[i];
                if(t[0] >= 0 && t[0] <rows && t[1] >=0 && t[1] < cols)
                    q.add(new int[]{t[0], t[1]});
            }
        }
        return res;
    }

    private static int sum(int x){
        int ret = 0;
        while(x !=0 ){
            ret += x%10;
            x /= 10;
        }
        return ret;
    }
}

方法二

bfs。

java代码

class Solution {

    int[] dx = new int[]{-1, 0, 1, 0};
    int[] dy = new int[]{0, 1, 0, -1};


    public int movingCount(int threshold, int rows, int cols){
        
        boolean[][] st = new boolean[rows][cols];
        return (dfs(threshold, 0, 0, st, rows, cols));
        
    }
    private int dfs(int threshold, int x, int y, boolean[][] st, int rows, int cols){
        if(x>=0 && x<rows && y>=0 && y<cols && sum(x)+sum(y)<=threshold && st[x][y]== false){
            int ret = 1;
            st[x][y] = true;
            for(int i=0; i<4; i++){
                int a = x+dx[i], b = y+dy[i];
                ret += dfs(threshold, a, b, st, rows, cols);
            }
            return ret;
        }
        return 0;
    }

    private static int sum(int x){
        int ret = 0;
        while(x !=0 ){
            ret += x%10;
            x /= 10;
        }
        return ret;
    }
}