---
tags: leetcode
---

# [366. Find Leaves of Binary Tree](https://leetcode.com/problems/find-leaves-of-binary-tree/)
---
# My Solution
## The Key Idea for Solving This Coding Question
DFS, recursion, post-order traversal
Assign each node a level.
## C++ Code

/**
 * 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<vector<int>> findLeaves(TreeNode *root) {
        vector<vector<int>> answer;

        dfs(root, answer);
        return answer;
    }

private:
    int dfs(TreeNode *root, vector<vector<int>> &answer) {
        if (root == nullptr) {
            return 0;
        }

        int leftLevel = dfs(root->left, answer);
        int rightLevel = dfs(root->right, answer);
        int rootLevel = max(leftLevel, rightLevel);
        if (answer.size() == rootLevel) {
            answer.push_back({});
        }
        answer[rootLevel].push_back(root->val);

        return rootLevel + 1;
    }
};

## Time Complexity
$O(n)$
$n$ is the number of nodes in the binary tree referred by `root`.
## Space Complexity
$O(H)$
$H$ is the height of the binary tree referred by `root`.
# Miscellaneous
[695. Max Area of Island](https://leetcode.com/problems/max-area-of-island/)
<!--
# Test Cases

[1,2,3,4,5]

[1]

[1,null,2,3]

[4,2,7,1,3]

[18,2,22,null,null,null,63,null,84,null,null]

[18,6,22,5,7,11,63,1,2,9,8,10,24,12,84]

[2,3,null,1]

[1,2,3]

[4,2,1,3,7]

[4,2,7,1,3,6,9]

[2,1,3]

-->