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WalkthroughA new Java class Changes
Sequence Diagram(s)sequenceDiagram
participant Caller
participant Solution
participant TreeNode
Caller->>Solution: levelOrder(root)
activate Solution
Solution->>Solution: traverse(root, 0)
activate Solution
rect rgb(200, 220, 255)
Note over Solution: At depth 0
Solution->>Solution: Create list for depth 0
Solution->>TreeNode: Access node value
Solution->>Solution: Add value to depth 0 list
end
Solution->>Solution: traverse(left, 1)
activate Solution
rect rgb(200, 220, 255)
Note over Solution: At depth 1
Solution->>Solution: Create list for depth 1
Solution->>TreeNode: Access left child value
Solution->>Solution: Add value to depth 1 list
end
deactivate Solution
Solution->>Solution: traverse(right, 1)
activate Solution
rect rgb(200, 220, 255)
Note over Solution: At depth 1
Solution->>TreeNode: Access right child value
Solution->>Solution: Add value to depth 1 list
end
deactivate Solution
deactivate Solution
Solution-->>Caller: Return List<List<Integer>>
deactivate Solution
Estimated code review effort🎯 2 (Simple) | ⏱️ ~8 minutes
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Pre-merge checks and finishing touches❌ Failed checks (1 warning, 1 inconclusive)
✅ Passed checks (1 passed)
✨ Finishing touches
🧪 Generate unit tests (beta)
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Actionable comments posted: 2
🧹 Nitpick comments (1)
Trees/Binary_Tree_Level.java (1)
27-39: Consider using iterative BFS for standard level-order traversal.The recursive DFS approach is correct and clever, but level-order traversal is typically implemented with iterative BFS using a queue. This would be more intuitive and could have better space complexity for skewed trees (O(w) queue space vs O(h) recursion stack, where w is max width and h is height).
If you prefer the standard approach, here's an iterative BFS implementation:
public List<List<Integer>> levelOrder(TreeNode root) { List<List<Integer>> res = new ArrayList<>(); if (root == null) { return res; } Queue<TreeNode> queue = new LinkedList<>(); queue.offer(root); while (!queue.isEmpty()) { int levelSize = queue.size(); List<Integer> level = new ArrayList<>(); for (int i = 0; i < levelSize; i++) { TreeNode node = queue.poll(); level.add(node.val); if (node.left != null) { queue.offer(node.left); } if (node.right != null) { queue.offer(node.right); } } res.add(level); } return res; }Note: This requires
import java.util.Queue;andimport java.util.LinkedList;
| package Trees; | ||
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| /** | ||
| * Definition for a binary tree node. | ||
| * public class TreeNode { | ||
| * int val; | ||
| * TreeNode left; | ||
| * TreeNode right; | ||
| * TreeNode() {} | ||
| * TreeNode(int val) { this.val = val; } | ||
| * TreeNode(int val, TreeNode left, TreeNode right) { | ||
| * this.val = val; | ||
| * this.left = left; | ||
| * this.right = right; | ||
| * } | ||
| * } | ||
| */ | ||
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There was a problem hiding this comment.
Add missing import statements.
The code uses List and ArrayList but the necessary import statements are missing, causing compilation failure.
Add these imports after the package declaration:
package Trees;
+
+import java.util.ArrayList;
+import java.util.List;
/**
* Definition for a binary tree node.📝 Committable suggestion
‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
| package Trees; | |
| /** | |
| * Definition for a binary tree node. | |
| * public class TreeNode { | |
| * int val; | |
| * TreeNode left; | |
| * TreeNode right; | |
| * TreeNode() {} | |
| * TreeNode(int val) { this.val = val; } | |
| * TreeNode(int val, TreeNode left, TreeNode right) { | |
| * this.val = val; | |
| * this.left = left; | |
| * this.right = right; | |
| * } | |
| * } | |
| */ | |
| package Trees; | |
| import java.util.ArrayList; | |
| import java.util.List; | |
| /** | |
| * Definition for a binary tree node. | |
| * public class TreeNode { | |
| * int val; | |
| * TreeNode left; | |
| * TreeNode right; | |
| * TreeNode() {} | |
| * TreeNode(int val) { this.val = val; } | |
| * TreeNode(int val, TreeNode left, TreeNode right) { | |
| * this.val = val; | |
| * this.left = left; | |
| * this.right = right; | |
| * } | |
| * } | |
| */ | |
🤖 Prompt for AI Agents
In Trees/Binary_Tree_Level.java around lines 1 to 18, the file uses List and
ArrayList but lacks the required imports; add the import statements for
java.util.List and java.util.ArrayList (or a single import java.util.*)
immediately after the package Trees; declaration so the code compiles.
| */ | ||
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| class Solution { | ||
| List<List<Integer>> res = new ArrayList<>(); |
There was a problem hiding this comment.
Fix reusability bug by making result a local variable.
The instance variable res causes incorrect behavior when levelOrder is called multiple times on the same Solution instance. The second call will append to the first call's results instead of starting fresh.
Move res to be a local variable in levelOrder and pass it to traverse:
class Solution {
- List<List<Integer>> res = new ArrayList<>();
public List<List<Integer>> levelOrder(TreeNode root) {
+ List<List<Integer>> res = new ArrayList<>();
- traverse(root, 0);
+ traverse(root, 0, res);
return res;
}
- private void traverse(TreeNode node, int depth) {
+ private void traverse(TreeNode node, int depth, List<List<Integer>> res) {
if (node == null) {
return;
}
if (res.size() == depth) {
res.add(new ArrayList<>());
}
res.get(depth).add(node.val);
- traverse(node.left, depth + 1);
- traverse(node.right, depth + 1);
+ traverse(node.left, depth + 1, res);
+ traverse(node.right, depth + 1, res);
}Committable suggestion skipped: line range outside the PR's diff.
🤖 Prompt for AI Agents
In Trees/Binary_Tree_Level.java around line 20, the instance field "res" causes
incorrect reuse across multiple levelOrder calls; make "res" a local variable by
removing the class-level declaration, instantiate List<List<Integer>> res = new
ArrayList<>() at the start of levelOrder, change traverse to accept this res as
a parameter (update its signature and all calls), and have traverse add levels
into the passed-in res; ensure levelOrder returns that local res so each call
starts with a fresh list.
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