1 files changed, 44 insertions, 0 deletions

diff --git a/top-interview-questions/easy/trees/04_binary_tree_level_order_traversal.cc b/top-interview-questions/easy/trees/04_binary_tree_level_order_traversal.cc
new file mode 100644
index 0000000..9c506ab
--- /dev/null
+++ b/top-interview-questions/easy/trees/04_binary_tree_level_order_traversal.cc
@@ -0,0 +1,44 @@
+/**
+ * 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:
+    void bfs(vector<vector<int>>& levels,
+             vector<const TreeNode*>& current_level,
+             vector<const TreeNode*>& next_level) {
+        if (current_level.empty()) {
+            return;
+        }
+        levels.push_back({});
+        vector<int>& level = levels.back();
+        level.reserve(current_level.size());
+        for (const TreeNode* node : current_level) {
+            level.push_back(node->val);
+            if (node->left) {
+                next_level.push_back(node->left);
+            }
+            if (node->right) {
+                next_level.push_back(node->right);
+            }
+        }
+        current_level.clear(); // New next level.
+        bfs(levels, next_level, current_level);
+    }
+
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        if (!root) return {};
+        vector<vector<int>> levels;
+        vector<const TreeNode*> current_level({root});
+        vector<const TreeNode*> next_level;
+        bfs(levels, current_level, next_level);
+        return levels;
+    }
+};