1325. Delete Leaves With a Given Value

/**
 * 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* removeLeafNodes(TreeNode* root, int target) {
    if (root == nullptr)
      return nullptr;
    root->left = removeLeafNodes(root->left, target);
    root->right = removeLeafNodes(root->right, target);
    return isLeaf(root) && root->val == target ? nullptr : root;
  }

 private:
  bool isLeaf(TreeNode* root) {
    return root->left == nullptr && root->right == nullptr;
  }
};