Create 0144-binary-tree-preorder-traversal.cpp

Author: Abe0770

Diff for: cpp/0144-binary-tree-preorder-traversal.cpp

@@ -0,0 +1,34 @@
+/*
+  Given the root of a binary tree, return the preorder traversal of its nodes' values.
+
+  Ex. Input: root = [1,null,2,3]
+      Output: [1,2,3]
+
+  Time  : O(N)
+  Space : O(H) -> H = Height of the binary tree
+*/
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    vector <int> res;
+
+    vector<int> preorderTraversal(TreeNode* root) {
+        if(root != NULL) {
+            res.push_back(root -> val);
+            preorderTraversal(root -> left);
+            preorderTraversal(root -> right);
+        }
+        return res;
+    }
+};