Leetcode 1457. Pseudo-Palindromic Paths in a Binary Tree

Count root-to-leaf paths in a binary tree of digits (1–9) that can be permuted into a palindrome — equivalently, paths whose digit counts have at most one odd frequency. With up to 1e5 nodes, this is solved by DFS while tracking parity of counts (e.g., a 9-bit mask) along each path.