【基础算法练习题】蓄水池问题

#include <bits/stdc++.h>
#define int long long
using namespace std;
int n;
int a[305][305];
// first -高度，second 位置
priority_queue<pair<int, pair<int, int>>> q;
bool vis[305][305];
int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, 1, -1};
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
        {
            cin >> a[i][j];
            if (i == 1 || j == 1 || i == n || j == n)
            {
                vis[i][j] = true;
                q.push(make_pair(-a[i][j], make_pair(i, j)));
            }
        }
    int ans = 0;
    while (!q.empty())
    {
        auto now = q.top();
        q.pop();
        int height = -now.first;
        int x = now.second.first;
        int y = now.second.second;
        for (int fx = 0; fx < 4; fx++)
        {
            int nx = x + dx[fx];
            int ny = y + dy[fx];
            if (nx < 1 || nx > n || ny < 1 || ny > n || vis[nx][ny])
                continue;
            if (height > a[nx][ny])
            {
                ans += height - a[nx][ny];
                a[nx][ny] = height;
            }
            vis[nx][ny] = true;
            q.push(make_pair(-a[nx][ny], make_pair(nx, ny)));
        }
    }
    cout << ans << "\n";
    return 0;
}