Given a Dictionary as value lists, inverse it, i.e map elements in list to keys and create new values list.
Input : test_dict = {1: [2, 3], 2: [3], 3: [1]} Output : {2: [1], 3: [1, 2], 1: [3]} Explanation : List elements mapped with their keys. Input : test_dict = {1: [2, 3, 4]} Output : {2: [1], 3: [1], 4: [1]} Explanation : List elements mapped with their keys.
Method : Using defaultdict() + loop
This is a way in which this task can be performed. In this, we initialize result keys with dictionary list, and iterate using loop to assign each value its keys, and reform the result dictionary values list.
Python3
# Python3 code to demonstrate working of # Inverse Dictionary Values List# Using from collections import defaultdict# initializing dictionarytest_dict = {1: [2, 3], 2: [3], 3: [1], 4: [2, 1]}# printing original dictionaryprint("The original dictionary is : " + str(test_dict))# initializing empty list as Valuesres = defaultdict(list) # using loop to perform reverse mappingfor keys, vals in test_dict.items(): for val in vals: res[val].append(keys)# printing result print("The required result : " + str(dict(res))) |
The original dictionary is : {1: [2, 3], 2: [3], 3: [1], 4: [2, 1]}
The required result : {2: [1, 4], 3: [1, 2], 1: [3, 4]}
Time Complexity: O(n*n) where n is the number of elements in the dictionary
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the dictionary
