[AcWing 1097] 池塘计数

Flood Fill 问题

---

点击查看代码

#include<bits/stdc++.h>

using namespace std;

typedef long long LL;

const int N = 1000 + 10;

#define x first
#define y second

int n, m;
char g[N][N];
bool st[N][N];

void bfs(int x, int y)
{
    queue<pair<int,int>> q;
    q.push({x, y});
    st[x][y] = true;
    while (q.size()) {
        auto 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 (t.x == i && t.y == j)
                    continue;
                if (i < 1 || i > n || j < 1 || j > m)
                    continue;
                if (g[i][j] == '.' || st[i][j])
                    continue;
                q.push({i, j});
                st[i][j] = true;
            }
    }
}

void solve()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i ++)
        for (int j = 1; j <= m; j ++)
            cin >> g[i][j];
    int res = 0;
    for (int i = 1; i <= n; i ++)
        for (int j = 1; j <= m; j ++)
            if (g[i][j] == 'W' && !st[i][j]) {
                bfs(i, j);
                res ++;
            }
    cout << res << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    solve();

    return 0;
}

---

1. 当枚举到有水的格子且格子未被标记，在这个位置开始 $BFS$，把所有和它属于同一片池塘的格子都标记上