B - Red and Black 问题思考

红黑地板问题

There is a rectangular room, covered with square tiles. Each tile is colored either red or black. A man is standing on a black tile. From a tile, he can move to one of four adjacent tiles. But he can't move on red tiles, he can move only on black tiles.

Write a program to count the number of black tiles which he can reach by repeating the moves described above.

Input

The input consists of multiple data sets. A data set starts with a line containing two positive integers W and H; W and H are the numbers of tiles in the x- and y- directions, respectively. W and H are not more than 20.

There are H more lines in the data set, each of which includes W characters. Each character represents the color of a tile as follows.

'.' - a black tile
'#' - a red tile
'@' - a man on a black tile(appears exactly once in a data set)
The end of the input is indicated by a line consisting of two zeros.

Output

For each data set, your program should output a line which contains the number of tiles he can reach from the initial tile (including itself).

Sample Input

6 9
....#.
.....#
......
......
......
......
......
#@...#
.#..#.
11 9
.#.........
.#.#######.
.#.#.....#.
.#.#.###.#.
.#.#..@#.#.
.#.#####.#.
.#.......#.
.#########.
...........
11 6
..#..#..#..
..#..#..#..
..#..#..###
..#..#..#@.
..#..#..#..
..#..#..#..
7 7
..#.#..
..#.#..
###.###
...@...
###.###
..#.#..
..#.#..
0 0

Sample Output

45
59
6
13
题目大意就是给定一个矩阵图形，初始位置为@，只能走. 不能走#，问最多能走多少. 
这是一道基础的dfs，bfs水题，然而，刚接触dfs和bfs的萌新敲得就很难受，看到这题，首先反应过来的就是用bfs解决，上下左右四个方向遍历，走过的就不能再走，好吧，写了两个bfs,第一个不知道哪错了，先放上WR代码吧
WR：把走过的点直接变为#，把要走的位置存入队列，计数，输出

#include <iostream>
#include <cstdio>
#include <string>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#pragma warning(disable:4996)
using namespace std;
//char a[105][105];
int main()
{
    int n, m;
    while (cin >> n >> m && n != 0 && m != 0)
    {
        char a[105][105];
        memset(a,0,sizeof(a));
        queue<int>p;
        int t1, t2;
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
            {
                cin >> a[i][j];
                if (a[i][j] == '@')
                {
                    t1 = i;
                    t2 = j;
                    p.push(t1);
                    p.push(t2);

                }
            }
        int num = 0, x, y;
        while (p.empty() == false)
        {
            x = p.front();
            p.pop();
            y = p.front();
            p.pop();
            num++;
            //cout << num << endl;
            if (0 <= x - 1 < m && 0 <= y < n  && a[x - 1][y] == '.')//上
            {
                p.push(x - 1);
                p.push(y);
                a[x - 1][y] = '#';
            }
            if (0 <= x + 1 < m && 0 <= y < n  && a[x + 1][y] == '.')//下
            {
                p.push(x + 1);
                p.push(y);
                a[x + 1][y] = '#';
            }
            if (0 <= x < m && 0 <= y - 1 < n && a[x][y - 1] == '.')//左
            {
                p.push(x);
                p.push(y - 1);
                a[x][y - 1] = '#';
            }
            if (0 <= x < m && 0 <= y + 1 < n && a[x][y + 1] == '.')//右
            {
                p.push(x);
                p.push(y + 1);
                a[x][y + 1] = '#';
            }
        }
        cout << num << endl;
    }
    return 0;
}

呜呜呜`~实在不知道哪错了

下面是一种采用标记方法的做法

AC：对走过的点进行标记，用visit数组储存访问状态，结构体储存位置存入队列（结构体在bfs中非常实用），bfs基础写法，，，

#include "pch.h"
#include <iostream>
#include <cstdio>
#include <string>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#pragma warning(disable:4996)
using namespace std;
int bfs(int x, int y);
struct point
{
    int x, y;
}s, s1;
char a[25][25];
int visit[105][105], n, m;
queue<point>p;
int direct[4][2] = { {-1,0},{1,0},{0,-1},{0,1} };

bool check(int x, int y)
{
    if (0 <= x && x < m && 0 <= y && y < n && visit[x][y]==0 && a[x][y] == '.')
        return true;
    else
        return false;
}
int bfs(int x, int y)
{
    visit[x][y] = 1;
    int sum = 0;
    while (!p.empty())
    {
        s1 = p.front();
        int t1 = s1.x;
        int t2 = s1.y;
        sum++;
        p.pop();
        for (int i = 0; i < 4; i++)
        {
            s1.x = t1 + direct[i][0];
            s1.y = t2 + direct[i][1];
        
            if (check(s1.x, s1.y))
            {
                visit[s1.x][s1.y] = 1;
                p.push(s1);
            
            }

        }
    }
    return sum;
}
int main()
{
    while (cin >> n >> m && n != 0 && m != 0)
    {
        memset(visit, 0, sizeof(visit));
        memset(a, 0, sizeof(a));
        int num = 1;
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
            {
                cin >> a[i][j];
                if (a[i][j] == '@')
                {
                    s.x = i;
                    s.y = j;
                    p.push(s);
                    
                }
            }
        num = bfs(s.x, s.y);
        cout << num << endl;

    }
    return 0;
}

目前还没想明白哪不一样，哎，呜呜呜

B - Red and Black 问题思考

猜你喜欢