Question

I’m implementing a disjoint set system in Python, but I’ve hit a wall. I’m using a tree implementation for the system and am implementing Find(), Merge() and Create() functions for the system.

I am implementing a rank system and path compression for efficiency.

The catch is that these functions must take the set of disjoint sets as a parameter, making traversing hard.

class Node(object):
    def __init__(self, value):
        self.parent = self
        self.value = value
        self.rank = 0

def Create(values):
    l = [Node(value) for value in values]
    return l

The Create function takes in a list of values and returns a list of singular Nodes containing the appropriate data.

I’m thinking the Merge function would look similar to this,

def Merge(set, value1, value2):
    value1Root = Find(set, value1)
    value2Root = Find(set, value2)
    if value1Root == value2Root:
        return
    if value1Root.rank < value2Root.rank:
        value1Root.parent = value2Root
    elif value1Root.rank > value2Root.rank:
        value2Root.parent = value1Root
    else:
        value2Root.parent = value1Root
        value1Root.rank += 1

but I’m not sure how to implement the Find() function since it is required to take the list of Nodes and a value (not just a node) as the parameters. Find(set, value) would be the prototype.

I understand how to implement path compression when a Node is taken as a parameter for Find(x), but this method is throwing me off.

Any help would be greatly appreciated. Thank you.

Edited for clarification.

Answer 1

Clearly merge function should be applied to pair of nodes.

So find function should take single node parameter and look like this:

def find(node):
    if node.parent != node:
        node.parent = find(node.parent)
    return node.parent

Also wikipedia has pseudocode that is easily translatable to python.