Adding a custom object to a Priority queue in Python

Issue

I want to add Node objects to Python’s PriorityQueue in Python 2. The Node objects should be prioritized according to the val attribute:

class ListNode:
     def __init__(self, val=0, next=None):
         self.val = val
         self.next = next

I am not allowed to tamper with this ListNode class so I do not have the option to add the __lt__ method to it.

Solution

You should be able to use a tuple to put the priority and the object in the PriorityQueue. Try:

pq = PriorityQueue()
ln2 = ListNode(2)
ln = ListNode(1, ln2)
pq.put((ln.val, ln))
pq.put((ln2.val, ln2)) 

Answered By – Bret Hogg

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