# Leetcode 606 - Construct String from Binary Tree

`Note:`

- Given traveral is in
`level order traversal`

. - Normally it’d be quite easy, but when do we need to
`omit ()`

and when not? - Ask ourself when do we
`need null`

in our input?- Ans: when we need to tell machine that
`left subtree`

is`empty`

and the`next node`

is for`right subtree`

.

- Ans: when we need to tell machine that
- So in our recursion, when a
`node has no left subtree`

but`has right subtree`

, we cannot omit`()`

.

`Question:`

Given the `root`

of a binary tree, construct a string consisting of parenthesis and integers from a binary tree with the preorder traversal way, and return it.

Omit all the empty parenthesis pairs that do not affect the one-to-one mapping relationship between the string and the original binary tree.

`Example:`

1 | Input: root = [1,2,3,4] |

1 | Input: root = [1,2,3,null,4] |

`Code:`

1 | /** |