1457 - Pseudo-Palindromic Paths in a Binary Tree.

Medium

Given a binary tree where node values are digits from 1 to 9. A path in the binary tree is said to be pseudo-palindromic if at least one permutation of the node values in the path is a palindrome.

Return the number of pseudo-palindromic paths going from the root node to leaf nodes.

Example 1:

Input: root = 2,3,1,3,1,null,1

Output: 2

Explanation: The figure above represents the given binary tree. There are three paths going from the root node to leaf nodes: the red path 2,3,3, the green path 2,1,1, and the path 2,3,1. Among these paths only red path and green path are pseudo-palindromic paths since the red path 2,3,3 can be rearranged in 3,2,3 (palindrome) and the green path 2,1,1 can be rearranged in 1,2,1 (palindrome).

Example 2:

Input: root = 2,1,1,1,3,null,null,null,null,null,1

Output: 1

Explanation: The figure above represents the given binary tree. There are three paths going from the root node to leaf nodes: the green path 2,1,1, the path 2,1,3,1, and the path 2,1. Among these paths only the green path is pseudo-palindromic since 2,1,1 can be rearranged in 1,2,1 (palindrome).

Example 3:

Input: root = 9

Output: 1

Constraints:

• The number of nodes in the tree is in the range <code>1, 10⁵</code>.

• 1 <= Node.val <= 9