Reverse lexicographical using heapq

Question

Essentially I am looking for an efficient way to implement custom comparators using heapq.

For instance x = [('a',5),('c',3),('d',2),('e',1)]

I could heapify it heapq.heapify(x) then pop the min value heapq.heappop(x) which would return ('a', 5). How can I make it such that it returns in reverse lexicographical order ('e', 1)? I know the convention when it comes to numbers is simply multiply the first element of the tuple by -1. Are there simple tricks like that when it comes to strings? I know I could potentially implement a map from a to z ... z to a but it sounds cumbersome.

score 3 · Accepted Answer · answered Jan 28 '22 at 22:13

For numbers you would do something like this:

import heapq

x = [(1, 5), (3, 3), (4, 2), (5, 1)]
x = [(-a, b) for a, b in x]
heapq.heapify(x)
result = heapq.heappop(x)
result = (-result[0], result[1])

Similarly, I would do this with letters:

import heapq

x = [('a',5), ('c',3), ('d',2), ('e',1)]
x = [(-ord(a), b) for a, b in x]
heapq.heapify(x)
result = heapq.heappop(x)
result = (chr(-result[0]), result[1])

You may want to treat similarly also the second element of each tuple

Reverse lexicographical using heapq

1 Answers1