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Find Leaves of Binary Tree

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Description

https://leetcode.com/problems/find-leaves-of-binary-tree/

Solution

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> findLeaves(TreeNode* root) {
        vector<vector<int>> ret;
        helper(root, ret);
        return ret;
    }
    
    int helper(TreeNode* root, vector<vector<int>>& ret) {
        if (root == NULL) return -1;
        int height = max(helper(root->left, ret), 
                            helper(root->right, ret)) + 1;
        
        if (ret.size() <= height) ret.resize(height + 1);
        ret[height].push_back(root->val);
        return height;
    }
};