P1792 [国家集训队]种树

https://www.luogu.com.cn/record/88801338

Luogu/P1792/P1792.cpp

@@ -0,0 +1,58 @@
+#include <iostream>
+#include <functional>
+#include <queue>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int n, m, a[N], pre[N], suf[N], ans;
+bool vis[N];
+std::priority_queue<std::pair<int, int>> q;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    if (n / 2 < m) {
+        cout << "Error!" << endl;
+
+        exit(0);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+
+        pre[i] = i - 1 ? i - 1 : n;
+        suf[i] = i == n ? 1 : i + 1;
+
+        q.emplace(a[i], i);
+    }
+
+    for (int i = 1; i <= m; i++) {
+        while (!q.empty() && vis[q.top().second]) q.pop();
+
+        auto o = q.top();
+        q.pop();
+
+        vis[pre[o.second]] = vis[suf[o.second]] = true;
+        a[o.second] = a[pre[o.second]] + a[suf[o.second]] - a[o.second];
+        q.emplace(a[o.second], o.second);
+        ans += o.first;
+
+        pre[o.second] = pre[pre[o.second]];
+        suf[o.second] = suf[suf[o.second]];
+        pre[suf[o.second]] = o.second;
+        suf[pre[o.second]] = o.second;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}