Create tallest-billboard.cpp

Author: kamyu104

C++/tallest-billboard.cpp

@@ -0,0 +1,34 @@
+// Time:  O(n * 3^(n/2))
+// Space: O(3^(n/2))
+
+class Solution {
+public:
+    int tallestBillboard(vector<int>& rods) {
+        auto left = dp(rods.cbegin(), rods.cbegin() + rods.size() / 2);
+        auto right = dp(rods.cbegin() + rods.size() / 2, rods.cend());
+        int result = 0;
+        for (const auto& kvp : left) {
+            if (right.count(kvp.first)) {
+                result = max(result,
+                             left[kvp.first] + right[kvp.first] + kvp.first);
+            }
+        }
+        return result;
+    }
+                              
+private:
+    unordered_map<int, int> dp(vector<int>::const_iterator it,
+                               vector<int>::const_iterator end) {
+        unordered_map<int, int> lookup;
+        lookup[0] = 0;
+        for (; it != end; ++it) {
+            unordered_map<int, int> tmp(lookup);
+            for (const auto& kvp : tmp) {
+                lookup[kvp.first + *it] = max(lookup[kvp.first + *it], kvp.second);
+                lookup[abs(kvp.first - *it)] = max(lookup[abs(kvp.first - *it)],
+                                                   kvp.second + min(kvp.first, *it));
+            }
+        }
+        return lookup;
+    }
+};