Finish LuoguP2627.cpp: monotonic queue

Luogu/LuoguP2627.cpp

@@ -0,0 +1,26 @@
+// problem statement: https://www.luogu.com.cn/problem/P2627
+
+#include <bits/stdc++.h>
+
+constexpr int MAXN = 1e5 + 10;
+
+using namespace std;
+
+int n, k;
+long long sum[MAXN], dp[MAXN];
+deque<long long> dq;
+
+int main() {
+    ios::sync_with_stdio(false);
+    cin >> n >> k;
+    for (int i = 1; i <= n; i++) { cin >> sum[i]; sum[i] += sum[i - 1]; }
+    for (int i = 1; i <= n; i++) {
+        while (!dq.empty() && dp[i - 1] - sum[i] >= dp[dq.back()] - sum[dq.back() + 1]) { dq.pop_back(); }
+        dq.push_back(i - 1);
+        while (!dq.empty() && i - dq.front() - 1 > k) { dq.pop_front(); }
+        dp[i] = dp[dq.front()] - sum[dq.front() + 1] + sum[i];
+        if (i <= k) { dp[i] = max(dp[i], sum[i] - sum[max(0, i - k)]); }
+    }
+    cout << dp[n] << '\n';
+    return 0;
+}