Finding Root of Tree from List of Tuples

Question

I am having issues writing a function that finds the root of a tree represented as a list of tuples in python.

Tree:

[(39, 38), (80, 70), (39, 42), (80, 91), (37, 22), (37, 39), (42, 45), (48, 37), (91, 85), (48, 60), (60, 80), (60, 50)]

I researched how to use classes for this but not sure if there is any kind of clever way to do this.

Answer 1

Just find the tuple start that is not in any tuple end:

lst = [(39, 38), (80, 70), (39, 42), (80, 91), (37, 22), (37, 39), (42, 45), (48, 37), (91, 85), (48, 60), (60, 80), (60, 50)]

rt = set([t[0] for t in lst if not t[0] in [t[1] for t in lst]])

print(rt)  # nothing links to 48 so it must be the root

Output

{48}

You can assign the t[1] loop to a variable if desired:

lst1 = [t[1] for t in lst]  # all end nodes
rt = set([t[0] for t in lst if not t[0] in lst1])