1372. Longest ZigZag Path in a Binary Tree

longest-zig-zag-binary-tree.ts

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

enum Direction {
  RIGHT,
  LEFT,
};


function longestZigZag(root: TreeNode | null): number {
  const findLongestZigZag = (node: TreeNode | null, startingDirection: Direction, depth: number) => {
    if (!node) {
      return depth;
    }

    const right = findLongestZigZag(node.right, Direction.RIGHT, startingDirection === Direction.LEFT ? depth + 1 : 0);
    const left = findLongestZigZag(node.left, Direction.LEFT, startingDirection === Direction.RIGHT ? depth + 1 : 0);

    return Math.max(right, left);
  }

  const right = findLongestZigZag(root.right, Direction.RIGHT, 0); 
  const left = findLongestZigZag(root.left, Direction.LEFT, 0);

  return Math.max(right, left);
};