Create find-all-the-lonely-nodes.cpp

Author: kamyu104

C++/find-all-the-lonely-nodes.cpp

@@ -0,0 +1,60 @@
+// Time:  O(n)
+// Space: O(h)
+
+/**
+ * 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> getLonelyNodes(TreeNode* root) {
+        vector<int> result;
+        vector<TreeNode *> stk = {root};
+        while (!stk.empty()) {
+            auto node = stk.back(); stk.pop_back();
+            if (!node) {
+                continue;
+            }
+            if (node->left && !node->right) {
+                result.emplace_back(node->left->val);
+            } else if (node->right && !node->left) {
+                result.emplace_back(node->right->val);
+            }
+            stk.emplace_back(node->right);
+            stk.emplace_back(node->left);
+        }
+        return result;
+    }
+};
+
+// Time:  O(n)
+// Space: O(h)
+class Solution2 {
+public:
+    vector<int> getLonelyNodes(TreeNode* root) {
+        vector<int> result;
+        dfs(root, &result);
+        return result;
+    }
+
+private:
+    void dfs(TreeNode *node, vector<int> *result) {
+        if (!node) {
+            return;
+        }
+        if (node->left && !node->right) {
+            result->emplace_back(node->left->val);
+        } else if (node->right && !node->left) {
+            result->emplace_back(node->right->val);
+        }
+        dfs(node->left, result);
+        dfs(node->right, result);
+    }
+};