# How Does Recursion Work On Traversing Through A Binary Tree, And Counting The Number Of List Nodes?

## 30 July 2020 - 1 answer

I have trouble visualizing these following print and size functions from the following URL (https://repl.it/@flowerplowedup/SquigglyVerifiablePaint#main.c):

Let's suppose you enter the input sequence

``````4 8 2 7 9 1 3 -1
``````

You wind up with a tree that looks like this:

``````                           4
/ \
/   \
2     8
/ \   / \
1   3 7   9
``````

`print_ascending`'s execution will look something like this :

``````print_ascending( node(4) )
{
node(4) != NULL
print_ascending( node(4)->left == node(2) )
{
node(2) != NULL
print_ascending( node(2)->left == node(1) )
{
node(1) != NULL
print_ascending( node(1)->left == NULL )
{
NULL == NULL
return
}
print( 1 )
print_ascending( node(1)->right == NULL)
{
NULL == NULL
return
}
return
}
print( 2 )
print_ascending( node(2)->right == node(3))
{
node(3) != NULL
print_ascending( node(3)->left == NULL )
{
NULL = NULL
return
}
print( 3 )
print_ascending( node(3)->right == NULL )
{
NULL = NULL
return
}
}
print( 4 )
print_ascending( node(4)->right == node(8) )
{
node(8) != NULL
print_ascending( node(8)->left == node(7) )
{
node(7) != NULL
print_ascending( node(7)->left == NULL )
{
NULL == NULL
return
}
print( 7 )
print_ascending( node(7)->right == NULL )
{
NULL == NULL
return
}
return
}
print( 8 )
print_ascending( node(8)->right == node(9) )
{
node(9) != NULL
print_ascending( node(9)->left == NULL )
{
NULL == NULL
return
}
print( 9 )
print_ascending( node(9)->right == NULL )
{
NULL == NULL
return
}
return
}
return
}
return
}
return
}
return
``````

Hopefully that helps visualize what's going on, and what's going on in the `size` function as well. Recursion's one of those concepts that takes a while to wrap your head around.