merge.py

# -*- coding: utf-8 -*-
# Copyright (c) 2019, Silvio Peroni <essepuntato@gmail.com>
#
# Permission to use, copy, modify, and/or distribute this software for any purpose
# with or without fee is hereby granted, provided that the above copyright notice
# and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
# FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT,
# OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
# DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
# ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
# SOFTWARE.


# Test case for the algorithm
def test_merge(left_list, right_list, expected):
    result = merge(left_list, right_list)
    if expected == result:
        return True
    else:
        return False


# Code of the algorithm
def merge(left_list, right_list):
    result = list()

    # Repeat until both lists have at least one item
    while len(left_list) > 0 and len(right_list) > 0:
        left_item = left_list[0]
        right_item = right_list[0]

        # If the item in left_list is less than the one in right_list,
        # add the formed to the result and remove it from left_list
        if left_item < right_item:
            result.append(left_item)
            left_list.remove(left_item)
        # Otherwise, the item in right_list is added to the result and
        # removed from the right_list
        else:
            result.append(right_item)
            right_list.remove(right_item)

    # Add to the result the remaining items from the lists
    result.extend(left_list)
    result.extend(right_list)

    return result


print(test_merge([], [], []))
print(test_merge([1, 2, 2, 3], [], [1, 2, 2, 3]))
print(test_merge([1, 2, 2, 3], [2, 3, 7], [1, 2, 2, 2, 3, 3, 7]))
print(test_merge(["Coraline", "Good Omens", "The Graveyard Book"],
                 ["American Gods", "Neverwhere"],
                 ["American Gods", "Coraline", "Good Omens", "Neverwhere", "The Graveyard Book"]))