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.

Constraints:

• The number of nodes in the tree will be in the range [1, 2500].
• The number of nodes in the list will be in the range [1, 100].
• 1 <= Node.val <= 100 for each node in the linked list and binary tree.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSubPath(ListNode head, TreeNode root) {
         if (root == null) {
            return false;
        }
        return isSubPathHelper(head, root) || isSubPath(head, root.left) || isSubPath(head, root.right);
    }

    private boolean isSubPathHelper(ListNode head, TreeNode node) {
        if (head == null) {
            return true;
        }
        if (node == null) {
            return false;
        }
        if (head.val != node.val) {
            return false;
        }
        return isSubPathHelper(head.next, node.left) || isSubPathHelper(head.next, node.right);
    }
}

1. The isSubPath method checks if the current node in the tree matches the node in the linked list. If there is a match, it recursively checks the left and right subtrees.
2. The isSubPathHelper method is used to traverse both the linked list and the binary tree. It returns true if we have reached the end of the linked list (indicating the path exists in the tree), false if we have reached the end of the tree (but not the linked list), and false if the values don't match.
3. By making the necessary comparisons and traversing both the linked list and the binary tree, the solution can accurately determine whether the linked list represents a subpath in the given binary tree.