# Postorder Successor

Moderate
0/80
Average time to solve is 15m

## Problem statement

You are given a binary tree having ‘N’ distinct nodes and an integer ‘M’, you have to return the postorder successor of ‘M’.

Note:

``````The postorder successor of ‘M’ is defined as the next element to ‘M’ in the sequence of postorder traversal.

If the postorder traversal of a tree is 3 5 4 7 then the postorder successor of 5 is the next element to 5 i.e 4.

Return ‘-1’ if there is no postorder successor of ‘M’.
``````
Detailed explanation ( Input/output format, Notes, Images )

#### Sample Input:

``````1
1 2 3 -1 -1 -1 -1
3
``````

#### Sample Output:

``````1
``````

#### Explanation:

``````The postorder traversal of the tree is 2 3 1. So the postorder successor of 3 is 1.
``````

#### Sample Input 2:

``````1
1 2 3 -1 4 -1 -1 5 6 -1 -1 -1 -1
5
``````

#### Sample Output 2:

``````6
``````

#### Explanation:

``````The postorder traversal of the tree is 5 6 4 2 3 1. So the postorder successor of 5 is 6.
``````
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