814. Binary Tree Pruning 2.cpp

// https://leetcode.com/problems/binary-tree-pruning/

/**
 * 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:
    TreeNode *pruneTree(TreeNode *root)
    {
        dfs(root);
        return root;
    }

    void dfs(TreeNode *&root)
    {
        if (root == nullptr)
            return;

        dfs(root->left);
        dfs(root->right);

        if (root->val == 0 && root->left == nullptr && root->right == nullptr)
            root = nullptr;
    }
};