Create make_tree for the fixed binary tree of the example.

leetcode/404.cpp

@@ -1,5 +1,4 @@
-#include <memory>
-#include <vector>
+#include <stdexcept>
 
 #include <gtest/gtest.h>
 
@@ -19,23 +18,14 @@ int sumOfLeftLeaves(TreeNode *root) {
 }
 
 TEST(sumOfLeftLeaves, SampleInput) {
-  auto root{std::make_unique<TreeNode>(3)};
-
-  // FIXME const construction.
-  std::vector<std::unique_ptr<TreeNode>> otherNodes;
-  otherNodes.push_back(std::make_unique<TreeNode>(9));
-  otherNodes.push_back(std::make_unique<TreeNode>(20));
-  otherNodes.push_back(std::make_unique<TreeNode>(15));
-  otherNodes.push_back(std::make_unique<TreeNode>(7));
-
-  root->left = otherNodes[0].get();
-  root->right = otherNodes[1].get();
-  root->right->left = otherNodes[2].get();
-  root->right->right = otherNodes[3].get();
-
+  const auto& [root, _] = make_tree({3, 9, 20, 15, 7});
   EXPECT_EQ(sumOfLeftLeaves(root.get()), 24);
 }
 
+TEST(make_tree, EmptyVector) {
+  EXPECT_THROW(static_cast<void>(make_tree({})), std::out_of_range);
+}
+
 int main(int argc, char **argv) {
   ::testing::InitGoogleTest(&argc, argv);
   return RUN_ALL_TESTS();

leetcode/tree.h

@@ -1,9 +1,37 @@
 #pragma once
 
+#include <memory>
+#include <utility>
+#include <vector>
+
+using std::pair;
+using std::make_unique;
+using std::unique_ptr;
+using std::vector;
+
 struct TreeNode {
   int val;
   TreeNode *left;
   TreeNode *right;
   TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 };
 
+pair<unique_ptr<TreeNode>, vector<unique_ptr<TreeNode>>>
+make_tree(const vector<int>& v) {
+  auto root{std::make_unique<TreeNode>(v.at(0))};
+
+  // FIXME const construction.
+  vector<unique_ptr<TreeNode>> otherNodes;
+  //TODO use actual data in v to construct the tree.
+  otherNodes.push_back(make_unique<TreeNode>(9));
+  otherNodes.push_back(make_unique<TreeNode>(20));
+  otherNodes.push_back(make_unique<TreeNode>(15));
+  otherNodes.push_back(make_unique<TreeNode>(7));
+
+  root->left = otherNodes[0].get();
+  root->right = otherNodes[1].get();
+  root->right->left = otherNodes[2].get();
+  root->right->right = otherNodes[3].get();
+
+  return std::make_pair(std::move(root), std::move(otherNodes));
+}