#687 - Longest Univalue Path

Medium • View on LeetCode • View on GitHub

Problem Description

Given the root of a binary tree, return the length of the longest path, where each node in the path has the same value. This path may or may not pass through the root.

The length of the path between two nodes is represented by the number of edges between them.

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var longestUnivaluePath = function(root) {
  let max = 0;
  dfs(root);
  return max;

  function dfs(node) {
    if (!node) return 0;

    const left = dfs(node.left);
    const right = dfs(node.right);
    const leftPath = node.left?.val === node.val ? left + 1 : 0;
    const rightPath = node.right?.val === node.val ? right + 1 : 0;

    max = Math.max(max, leftPath + rightPath);
    return Math.max(leftPath, rightPath);
  }
};