Btree preorder traversal (#181)

* add btree preorder traversal

* impl btree preorder traversal

leetcode-cc/BTreePreorderTraversal.hpp

@@ -0,0 +1,49 @@
+#include <stack>
+
+#include "TestHelper.h"
+#include "problem.h"
+#include "solution.h"
+
+using namespace std;
+
+IMPLEMENT_PROBLEM_CLASS(PBTreePreorderTraversal, 144, DIFFI_MEDIUM,
+                        TOPIC_ALGORITHMS, "Binary Tree Preorder Traversal",
+                        "Given the root of a binary tree, return the preorder "
+                        "traversal of its nodes' values.",
+                        {"Binary Tree"});
+
+class SBTreePreorderTraversal : public ISolution {
+ public:
+  size_t problemId() const override { return 144; }
+  string name() const override {
+    return ("Solution for " + string("Binary Tree Preorder Traversal"));
+  }
+  string location() const override { return __FILE_NAME__; }
+  int test() const override {
+    return testHelperBinaryTreeV2<vector<int>>(
+        {"[1,null,2,3]", "[]", "[1]"}, {{1, 2, 3}, {}, {1}},
+        [this](auto root) { return this->preorderTraversal(root); });
+  };
+  int benchmark() const override { return 0; }
+
+ private:
+  vector<int> preorderTraversal(TreeNode* root) const {
+    stack<TreeNode*> s = {};
+    auto node = root;
+    vector<int> res;
+
+    while (node || !s.empty()) {
+      if (node) {
+        res.push_back(node->val);
+        s.push(node);
+        node = node->left;
+      } else {
+        auto parent = s.top();
+        s.pop();
+        node = parent->right;
+      }
+    }
+
+    return res;
+  }
+};

runtime-cc/src/registration.cc

@@ -2,6 +2,7 @@
 
 #include "../leetcode-cc/BTreeLevelTraversalII.hpp"
 #include "../leetcode-cc/BTreeMaxPathSum.hpp"
+#include "../leetcode-cc/BTreePreorderTraversal.hpp"
 #include "../leetcode-cc/BTreeZigzagLevelOrderTraversal.hpp"
 #include "../leetcode-cc/BalancedBTree.hpp"
 #include "../leetcode-cc/BestTimeToBuySellStockIII.hpp"
@@ -605,5 +606,12 @@ const int registerAll(std::shared_ptr<Container> handle) {
   handle->registerSolution(
       []() -> ArcSolution { return std::make_shared<SReorderList>(); });
 
+  handle->registerProblem([]() -> ArcProblem {
+    return std::make_shared<PBTreePreorderTraversal>();
+  });
+  handle->registerSolution([]() -> ArcSolution {
+    return std::make_shared<SBTreePreorderTraversal>();
+  });
+
   return 0;
 }