AcWing 1113. 红与黑【《信息学奥赛一本通》】【DFS】【BFS】【Flood Fill】一、题目链接二、题目分析三、AC代码四、其它题解

1
2
3
4
5
6
int m, n;
while (cin >> m >> n, m || n)
{
    
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>

using namespace std;

typedef pair<int, int> PII;
#define x first
#define y second

const int N = 25;

char g[N][N];
bool st[N][N];

int n, m;

int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

int bfs(PII start)
{
    memset(st, false, sizeof st);
    // 当前点遍历过
    st[start.x][start.y] = true;
    // 当前点也是黑色
    int cnt = 1;
    queue<PII> q;
    q.push(start);
    
    while (!q.empty())
    {
        auto t = q.front();
        q.pop();
        
        for (int i = 0; i < 4; i ++ )
        {
            int x = t.x + dx[i], y = t.y + dy[i];
            if (x < 0 || x >= n || y < 0 || y >= m) continue;
            if (g[x][y] == '.' && !st[x][y]) 
            {
                cnt ++ ;
                st[x][y] = true;
                q.push({x, y});
            }
        }
    }
    return cnt;
}
int main()
{
    while (true)
    {
        cin >> m >> n;
        if (m == 0) break;
        for (int i = 0; i < n; i ++ ) scanf("%s", g[i]);
        
        PII start;
        for (int i = 0; i < n; i ++ )
            for (int j = 0; j < m; j ++ )
                if (g[i][j] == '@')
                {
                    start = {i, j};
                    break;
                }
        
        cout << bfs(start) << endl;
    }
    return 0;
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

typedef pair<int, int> PII;
#define x first
#define y second

const int N = 25;

char g[N][N];
bool st[N][N];

int n, m;

int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

int dfs(int x, int y)
{
    int cnt = 1;
    st[x][y] = true;
    
    for (int i = 0; i < 4; i ++ )
    {
        int a = x + dx[i], b = y + dy[i];
        if (a < 0 || a >= n || b < 0 || b >= m) continue;
        
        if (!st[a][b] && g[a][b] == '.')
        {
            cnt += dfs(a, b);
        }
    }
    return cnt;
}
int main()
{
    while (true)
    {
        cin >> m >> n;
        if (m == 0) break;
        for (int i = 0; i < n; i ++ ) scanf("%s", g[i]);
        
        int x, y;
        for (int i = 0; i < n; i ++ )
            for (int j = 0; j < m; j ++ )
                if (g[i][j] == '@')
                {
                    x = i, y = j;
                    break;
                }
        memset(st, false, sizeof st);
        cout << dfs(x, y) << endl;
    }
    return 0;
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

typedef pair<int, int> PII;
#define x first
#define y second

const int N = 25;

char g[N][N];
bool st[N][N];

int n, m;

int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

// 另一种dfs写法
int ans;
void dfs(int x, int y)
{
    // 如果跑出图了就返回
    if (x < 0 || x >= n || y < 0 || y >= m) return;
    // 标记当前点已经搜索过
    st[x][y] = true;
    // 每跑一次dfs就代表进来一个新的没跑过的黑格子，所以答案要加一
    ans ++ ;
    for (int i = 0; i < 4; i ++ )
    {
        int a = x + dx[i], b = y + dy[i];
        if (a < 0 || a >= n || b < 0 || b >= m) continue;
        
        if (!st[a][b] && g[a][b] == '.')
        {
            dfs(a, b);
        }
    }
}

int main()
{
    while (true)
    {
        cin >> m >> n;
        if (m == 0) break;
        for (int i = 0; i < n; i ++ ) scanf("%s", g[i]);
        
        int x, y;
        for (int i = 0; i < n; i ++ )
            for (int j = 0; j < m; j ++ )
                if (g[i][j] == '@')
                {
                    x = i, y = j;
                    break;
                }
        memset(st, false, sizeof st);

        ans = 0;
        dfs(x, y);
        cout << ans << endl;
    }
    return 0;
}