Converting a nested dictionary into Flattened dictionary

Question

Consider a nested dictionary as follows: {'Fruit': 1, 'Vegetable': {'Cabbage': 2, 'Cauliflower': 3}, 'Spices': 4} Your task is to flatten a nested dictionary and join the nested keys with the "_" character. For the above dictionary, the flattened dictionary would be as follows: {'Fruit': 1, 'Vegetable_Cabbage': 2, 'Vegetable_Cauliflower': 3, 'Spices': 4} The input will have a nested dictionary. The output should have two lists. The first list will have keys, and the second list should have values. Both lists should be sorted. Sample Input: {'Fruit': 1, 'Vegetable': {'Cabbage': 2, 'Cauliflower': 3}, 'Spices': 4}