Create boundary-of-binary-tree.cpp

Author: kamyu104

C++/boundary-of-binary-tree.cpp

@@ -0,0 +1,65 @@
+// Time:  O(n)
+// Space: O(h)
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<int> boundaryOfBinaryTree(TreeNode* root) {
+        if (!root) {
+            return {};
+        }
+
+        vector<int> nodes;
+        nodes.emplace_back(root->val);
+        leftBoundary(root->left, &nodes);
+        leaves(root->left, &nodes);
+        leaves(root->right, &nodes);
+        rightBoundary(root->right, &nodes);
+        return nodes;
+    }
+
+private:
+    void leftBoundary(TreeNode *root, vector<int> *nodes) {
+        if (!root || (!root->left && !root->right)) {
+            return;
+        }
+        nodes->emplace_back(root->val);
+        if (!root->left) {
+            leftBoundary(root->right, nodes);
+        } else {
+            leftBoundary(root->left, nodes);
+        }
+    }
+
+    void rightBoundary(TreeNode *root, vector<int> *nodes) {
+        if (!root || (!root->right && !root->left)) {
+            return;
+        }
+        if (!root->right) {
+            rightBoundary(root->left, nodes);
+        } else {
+            rightBoundary(root->right, nodes);
+        }
+        nodes->emplace_back(root->val);
+    }
+    
+    void leaves(TreeNode *root, vector<int> *nodes) {
+        if (!root) {
+            return;
+        }
+        if (!root->left && !root->right) {
+            nodes->emplace_back(root->val);
+            return;
+        }
+        leaves(root->left, nodes);
+        leaves(root->right, nodes);
+    }
+};