366. Find Leaves of Binary Tree

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366. Find Leaves of Binary Tree

Description

Given the root of a binary tree, collect a tree’s nodes as if you were doing this:

  • Collect all the leaf nodes.
  • Remove all the leaf nodes.
  • Repeat until the tree is empty.

Example 1:

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Input: root = [1,2,3,4,5]
Output: [[4,5,3],[2],[1]]
Explanation:
[[3,5,4],[2],[1]] and [[3,4,5],[2],[1]] are also considered correct answers since per each level it does not matter the order on which elements are returned.

Example 2:

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Input: root = [1]
Output: [[1]]

Constraints:

  • The number of nodes in the tree is in the range [1, 100].
  • -100 <= Node.val <= 100

Hints/Notes

  • N/A

Solution

Language: C++

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/**
 * 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>> res;

    vector<vector<int>> findLeaves(TreeNode* root) {
        traverse(root);
        return res;
    }

    int traverse(TreeNode* root) {
        if (!root) {
            return 0;
        }

        int leftDepth = traverse(root->left);
        int rightDepth = traverse(root->right);

        int depth = max(leftDepth, rightDepth) + 1;

        if (depth > res.size()) {
            res.push_back({root->val});
        } else {
            res[depth - 1].push_back(root->val);
        }

        return depth;
    }
};