Binary Tree Paths

Description

Given a binary tree, return all root-to-leaf paths.

Note: A leaf is a node with no children.

Example:

Input:
1
/   

2     3


5
Output: ["1->2->5", "1->3"]
Explanation: All root-to-leaf paths are: 1->2->5, 1->3

Solution(javascript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {string[]}
 */
const binaryTreePaths = (root) => {
  const isLeaf = node => node && (!node.left) && (!node.right)
  const join = (current, val) => (current ? `${current}->${val}` : `${val}`)
  const aux = (node, currentPath = '', acc) => {
    if (!node) {
      return acc
    }
    if (isLeaf(node)) {
      currentPath = join(currentPath, node.val)
      acc.push(currentPath)
    }
    aux(node.left, join(currentPath, node.val), acc)
    aux(node.right, join(currentPath, node.val), acc)
    return acc
  }
  return aux(root, '', [])
}