What is the relation between internal path length and external path length in a binary tree?

# Path length of Binary Tree

**atta_k**#2

In an external binary tree, all nodes have either 2 children or 0 children.

The nodes with two children are called internal nodes.

The nodes with zero child are called external nodes( “extended” nodes ).

**Internal path length(I)** is the summation of the lengths all of the lengths all paths from the root of a binary tree to each of its nodes.

**External path length(E)** is the summation of the lengths of path lengths to the “extended” nodes of a binary tree, usually the null nodes with zero children .

**E = I + 2n** (where **n** is the number of internal nodes)