# Find Leaves of Binary Tree

{% embed url="<https://www.lintcode.com/problem/650/>" %}

## Solution 1 (Java)

```java
/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param root: the root of binary tree
     * @return: collect and remove all leaves
     */
    public List<List<Integer>> findLeaves(TreeNode root) {
        List<List<Integer>> res = new ArrayList<>();
        Map<Integer, List<Integer>> levels = new HashMap<>();

        int maxDepth = dfs(root, levels);
        for (int i = 1; i <= maxDepth; i++) {
            res.add(levels.get(i));
        }
        return res;
    }

    private int dfs(TreeNode root, Map<Integer, List<Integer>> levels) {
        if (root == null) return 0;
        int maxDepth = Math.max(dfs(root.left, levels), dfs(root.right, levels)) + 1;
        // 1 is the bottom level
        levels.putIfAbsent(maxDepth, new ArrayList<>());
        levels.get(maxDepth).add(root.val);
        return maxDepth;
    }
}
```

### Notes

* Use a `HashMap` to store the levels of the tree. The key is the level (1 is the bottom level) and the value of a list of node values.
* Use a similar mechanism in [Maximum Depth of Binary Tree](/algo/binary-tree/2.-classical-questions/maximum-depth-of-binary-tree.md) and add a few operations to populate the map.&#x20;
* Lastly, convert the values in the map to a result list and return.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://blog.yushunchen.com/algo/binary-tree/1.-traversal/find-leaves-of-binary-tree.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.