#1611. 【2022.10.9 联考】和为贵（sum）

https://sjzezoj.com/submission/59820

S2OJ/1611/1611.cpp

@@ -0,0 +1,69 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+#include <set>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e5 + 5,
+          K = 55;
+
+int n, k, a[N], pos[N], pre[N][K], nxt[N][K], prev[N], next[N];
+long long ans;
+std::set<int> set;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> k;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+
+        pos[a[i]] = i;
+    }
+
+    for (int i = n; i; i--) {
+        int p = pos[i];
+        auto it = set.lower_bound(p);
+
+        std::fill_n(pre[p], K, 0);
+        std::fill_n(nxt[p], K, n + 1);
+        pre[p][0] = nxt[p][0] = p;
+
+        if (it != set.end()) {
+            prev[*it] = p;
+            next[p] = *it;
+
+            for (int j = *it, l = 1; j && l <= k; j = next[j], l++) {
+                nxt[p][l] = j;
+            }
+        }
+
+        if (it != set.begin()) {
+            it--;
+
+            prev[p] = *it;
+            next[*it] = p;
+
+            for (int j = *it, l = 1; j && l <= k; j = prev[j], l++) {
+                pre[p][l] = j;
+            }
+        }
+
+        set.insert(p);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= k; j++) {
+            ans += static_cast<long long>(a[i]) * (pre[i][j - 1] - pre[i][j]) * (nxt[i][k - j + 1] - nxt[i][k - j]);
+        }
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}