heapq.heapify(x) code example

Example: heapq python how to use comparator

class Solution:
    def mergeKLists(self, lists: List[ListNode]) -> ListNode:
        
        setattr(ListNode, "__lt__", lambda self, other: self.val <= other.val)
            
        pq = []
        for l in lists:
            if l:
                heapq.heappush(pq,  l)
        
        out = ListNode(None)
        head = out
        while pq:
            l = heapq.heappop(pq)
            head.next = l
            head = head.next
            if l and l.next:
                heapq.heappush( pq, l.next)
            
        return out.next