Flood Fill 问题

算法小菜第一次写题解,就是简单贴一下打卡代码,尝试一下,后面一定详细写

BFS

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
#include <queue>
#define x first
#define y second
using namespace std;

const int N = 1010, M = N * N;

typedef pair<int, int> PII;

int n, m;
PII q[M]; //模拟队列数组 
char g[N][N];
bool st[N][N];
/*模拟队列
void bfs(int sx, int sy)
{
    int hh = 0, tt = 0;
    q[0] = {sx, sy};
    st[sx][sy] = true;

    while (hh <= tt)
    {
        PII t = q[hh ++ ];

        for (int i = t.x - 1; i <= t.x + 1; i ++ )
            for (int j = t.y - 1; j <= t.y + 1; j ++ )
            {
                if (i == t.x && j == t.y) continue;
                if (i < 0 || i >= n || j < 0 || j >= m) continue;
                if (g[i][j] == '.' || st[i][j]) continue;

                q[ ++ tt] = {i, j};
                st[i][j] = true;
            }
    }
}*/

void bfs(int sx, int sy)
{
    queue<PII> q;
    q.push({sx, sy});
    st[sx][sy] = true;

    while (q.size())
    {
        PII t = q.front();
        q.pop();

        for (int i = t.x - 1; i <= t.x + 1; i ++ )
            for (int j = t.y - 1; j <= t.y + 1; j ++ )
            {
                if (i == t.x && j == t.y) continue;
                if (i < 0 || i >= n || j < 0 || j >= m) continue;
                if (g[i][j] == '.' || st[i][j]) continue;

                q.push({i, j});
                st[i][j] = true;
            }
    }
}

int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i ++ ) scanf("%s", g[i]);

    int cnt = 0;    
    for (int i = 0; i < n; i ++ )
        for (int j = 0; j < m; j ++ )
        {
            if (!st[i][j] && g[i][j] == 'W')
            {
                bfs(i, j);
                cnt ++;
            }
        }

    cout << cnt << endl;

    return 0;
}

DFS 借鉴大佬思路

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>

using namespace std;

const int N = 1010;

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

int n, m, cnt;
char g[N][N];

void dfs(int x, int y)
{
    for (int i = 0; i < 8; i ++ )
    {
        int tx = x + dx[i], ty = y + dy[i];
        if (tx < 0 || tx >= n || ty < 0 || ty >= m || g[tx][ty] == '.') continue;
        g[tx][ty] = '.'; //标记搜过并以该点为起始点
        dfs(tx, ty); 
    }
}

int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i ++ ) scanf("%s", &g[i]);

    for (int i = 0; i < n; i ++ )
        for (int j = 0; j < m; j ++ )
        {
            if (g[i][j] == 'W')
            {
                dfs(i, j);
                cnt ++;
            }
        }

    cout << cnt << endl;
    return 0;
}