# LeetCode 257. Binary Tree Paths

## Description

https://leetcode.com/problems/path-crossing/

Given the `root` of a binary tree, return all root-to-leaf paths in any order.

leaf is a node with no children.

Example 1:

```Input: root = [1,2,3,null,5]
Output: ["1->2->5","1->3"]
```

Example 2:

```Input: root = [1]
Output: ["1"]
```

Constraints:

• The number of nodes in the tree is in the range `[1, 100]`.
• `-100 <= Node.val <= 100`

## Explanation

Traverse the tree and track the root to leaf paths.

## Python Solution

``````# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def binaryTreePaths(self, root: TreeNode) -> List[str]:
self.results = []
if not root:
return self.results

self.traverse(root, [str(root.val)])

return self.results

def traverse(self, root, path):

if not root.left and not root.right:
path_str = "->".join(path)
self.results.append(path_str)
return

if root.left:
path.append(str(root.left.val))
self.traverse(root.left, path)
path.pop()

if root.right:
path.append(str(root.right.val))
self.traverse(root.right, path)
path.pop()``````
• Time Complexity: O(N).
• Space Complexity: O(N).