257. Binary Tree Paths

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

Analyze

• DFS 深度优先遍历的运用, 关键需要想清楚采用先序、中序、后序遍历中的哪一种。
  • 先序遍历: 1 -> 2 -> 5, 1 -> 3

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {string[]}
 */
var binaryTreePaths = function(root) {
  const result = []
  if (!root) return result

  printTreePaths(root, result, '')
  return result
}

var printTreePaths = function(node, result, str) {
  if (!node.left && !node.right) {
    str += `${node.val}`
    result.push(str)
    return
  }

  str += `${node.val}->`

  if (node.left) {
    printTreePaths(node.left, result, str)
  }

  if (node.right) {
    printTreePaths(node.right, result, str)
  }
}