23. Linked List in Binary Tree

Given a binary tree root and a linked list with head as the first node.

Return True if all the elements in the linked list starting from the head correspond to some downward path connected in the binary tree otherwise return False.

In this context downward path means a path that starts at some node and goes downwards.

Example 1:

Input: head = [4,2,8], root = [1,4,4,null,2,2,null,1,null,6,8,null,null,null,null,1,3]
Output: true
Explanation: Nodes in blue form a subpath in the binary Tree.  

Example 2:

Input: head = [1,4,2,6], root = [1,4,4,null,2,2,null,1,null,6,8,null,null,null,null,1,3]
Output: true

Example 3:

Input: head = [1,4,2,6,8], root = [1,4,4,null,2,2,null,1,null,6,8,null,null,null,null,1,3]
Output: false
Explanation: There is no path in the binary tree that contains all the elements of the linked list from head.

Solution: (Using Preorder Traversal)

class Solution
{
public:
    bool checkPath(TreeNode *root, ListNode *head)
    {
        if (head == NULL)
        {
            return true;
        }

        if (root == NULL)
        {
            return false;
        }

        bool res = false;
        if (head->val == root->val)
        {
            res = checkPath(root->left, head->next) || checkPath(root->right, head->next);
        }

        return res;
    }
    
    bool isSubPath(ListNode *head, TreeNode *root)
    {

        if (root == NULL)
        {
            return false;
        }

        if (root->val == head->val)
        {
            if (checkPath(root, head))
            {
                return true;
            }
        }

        bool res = isSubPath(head, root->left) || isSubPath(head, root->right);
        return res;
    }
};