Python | Inverse Sorting String

Sometimes, while participating in a competitive programming test, we can be encountered with a problem in which we require to sort a pair in opposite orders by indices. This particular article focuses on solving a problem in which we require to sort the number in descending order and then the String in increasing order. This is the type of problem which is common in the sorting of pairs. Let's discuss a way in which this can be solved. 

Method : Using sorted() + lambda The combination of these functions can be used to perform this task. In these, we pass to lambda function the negative of the values so that the increasing order of number is evaluated as decreasing and hence a successful hack to perform this task. 

# Python3 code to demonstrate working of
# Inverse sorting String, Integer tuple list
# Using sorted() + lambda

# initializing list
test_list = [("Geeks", 5), ("For", 3), ("Geeks", 6), ("Is", 5), 
             ("Best", 7 ), ("For", 5), ("CS", 3)]

# printing original list
print("The original list is : " + str(test_list))

# Inverse sorting String, Integer tuple list
# Using sorted() + lambda
res = sorted(test_list, key = lambda sub: (-sub[1], sub[0]))

# printing result 
print("The list after inverse sorted tuple elements : " + str(res))

Time Complexity: O(nlogn), where n is the length of the list test_list 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the res list 

Method: Using heapq module

Import the heapq module.
Initialize an empty list result.
Convert the given list into a min heap using the heapify() function of the heapq module.
Extract the elements from the heap one by one using the heappop() function of the heapq module.
Append the extracted element to the result list.
Return the result list.

import heapq

# initializing list
test_list = [("Geeks", 5), ("For", 3), ("Geeks", 6), ("Is", 5), 
             ("Best", 7 ), ("For", 5), ("CS", 3)]

# printing original list
print("The original list is : " + str(test_list))

# Inverse sorting String, Integer tuple list
# Using heapq module
result = []
heapq.heapify(test_list)
while test_list:
    result.append(heapq.heappop(test_list))

# printing result 
print("The list after inverse sorted tuple elements : " + str(result))

The original list is : [('Geeks', 5), ('For', 3), ('Geeks', 6), ('Is', 5), ('Best', 7), ('For', 5), ('CS', 3)]
The list after inverse sorted tuple elements : [('Best', 7), ('CS', 3), ('For', 3), ('For', 5), ('Geeks', 5), ('Geeks', 6), ('Is', 5)]

The time complexity of this approach is O(n log n) due to the heapification step. 

The auxiliary space used is O(n) to store the result list.