种树(Planting Trees) 题解

思路分析

按题目要求使用对应数据结构与算法模拟/递推求解，注意数据范围边界与时间复杂度。

参考代码

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, m;
    if (!(cin >> n >> m)) return 0;
    vector<long long> a(n);
    for (int i = 0; i < n; ++i) cin >> a[i];
    if (m > n / 2) {
        cout << "Error!\n";
        return 0;
    }
    vector<int> L(n), R(n);
    vector<bool> del(n, false);
    priority_queue<pair<long long, int>> pq;
    for (int i = 0; i < n; ++i) {
        L[i] = (i - 1 + n) % n;
        R[i] = (i + 1) % n;
        pq.push({a[i], i});
    }
    long long ans = 0;
    for (int step = 0; step < m; ++step) {
        while (!pq.empty() && del[pq.top().second]) pq.pop();
        auto [v, u] = pq.top();
        pq.pop();
        ans += v;
        int l = L[u], r = R[u];
        a[u] = a[l] + a[r] - a[u];
        del[l] = del[r] = true;
        L[u] = L[l];
        R[u] = R[r];
        R[L[u]] = u;
        L[R[u]] = u;
        pq.push({a[u], u});
    }
    cout << ans << "\n";
    return 0;
}