[AcWing 1106] 山峰和山谷

Flood Fill

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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;
int g[N][N];
bool st[N][N];
int dx[] = {0, -1, 0, 1};
int dy[] = {-1, 0, 1, 0};

void bfs(int x, int y, bool &high, bool &low)
{
    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 > n)
                    continue;
                if (g[i][j] != g[t.x][t.y]) {
                    if (g[i][j] > g[t.x][t.y])
                        high = true;
                    else
                        low = true;
                }
                else if (!st[i][j]) {
                    q.push({i, j});
                    st[i][j] = true;
                }
            }
    }
}

void solve()
{
    cin >> n;
    for (int i = 1; i <= n; i ++)
        for (int j = 1; j <= n; j ++)
            cin >> g[i][j];
    int peak = 0, valley = 0;
    for (int i = 1; i <= n; i ++)
        for (int j = 1; j <= n; j ++)
            if (!st[i][j]) {
                bool high = false, low = false;
                bfs(i, j, high, low);
                if (!high)
                    peak ++;
                if (!low)
                    valley ++;
            }
    cout << peak << ' ' << valley << endl;
}

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

    solve();

    return 0;
}

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1. 当遇到没有标记过的块时，对其做 \(BFS\)，同时记录周围有无更高的或者更低的，如果没有更高的，说明这一块所属的区域是山峰，如果没有更低的，说明这一块所属的区域是山谷