Create beautiful-towers-ii.cpp

Author: kamyu104

C++/beautiful-towers-ii.cpp

@@ -0,0 +1,33 @@
+// Time:  O(n)
+// Space: O(n)
+
+// mono stack
+class Solution {
+public:
+    long long maximumSumOfHeights(vector<int>& maxHeights) {
+        vector<int64_t> left(size(maxHeights));
+        vector<int64_t> stk = {-1};
+        for (int64_t i = 0, curr = 0; i < size(maxHeights); ++i) {
+            while (stk.back() != stk[0] && maxHeights[stk.back()] >= maxHeights[i]) {
+                const int j = stk.back(); stk.pop_back();
+                curr -= (j - stk.back()) * maxHeights[j];
+            }
+            curr += (i - stk.back()) * maxHeights[i];
+            stk.emplace_back(i);
+            left[i] = curr;
+        }
+        int64_t result = 0, right = 0;
+        stk = {static_cast<int64_t>(size(maxHeights))};
+        for (int64_t i = size(maxHeights) - 1, curr = 0; i >= 0; --i) {
+            while (stk.back() != stk[0] && maxHeights[stk.back()] >= maxHeights[i]) {
+                const int j = stk.back(); stk.pop_back();
+                curr -= (stk.back() - j) * maxHeights[j];
+            }
+            curr += (stk.back() - i) * maxHeights[i];
+            stk.emplace_back(i);
+            right = curr;
+            result = max(result, left[i] + right - maxHeights[i]);
+        }
+        return result;
+    }
+};