1325. Delete Leaves With a Given Value

Given a binary tree root and an integer target, delete all the leaf nodes with value target.

Note that once you delete a leaf node with value target, if its parent node becomes a leaf node and has the value target, it should also be deleted (you need to continue doing that until you cannot).

/**
 * 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 {
    bool isLeafTarget(TreeNode* node, int& target) {
        return node->val == target and node->left == nullptr and node->right == nullptr;
    }
    void travel(TreeNode* node, int& target) {
        if(node->left) {
            travel(node->left, target);
            if(isLeafTarget(node->left, target)) {
                node->left = nullptr;
            }
        }
        if(node->right) {
            travel(node->right, target);
            if(isLeafTarget(node->right, target)) {
                node->right = nullptr;
            }
        }
    }
public:
    TreeNode* removeLeafNodes(TreeNode* root, int target) {
        TreeNode* dummy = new TreeNode(-1, root, nullptr);
        travel(dummy, target);
        return dummy->left;
    }
};