def merge(lst1, lst2):
"""Merges two sorted lists `lst1` and `lst2`
Returns a sorted list where `lst1` and `lst2` are merged and deduplicated
"""
# Check if both lists are sorted (function sorted() in sortedList.py)
# Return false if the lists are not sorted
if not sortedList.sorted(lst1) or not sortedList.sorted(lst2):
return False
# The variable that will hold the merged list.
ret = []
# While both lists still have elements...
while len(lst1) > 0 and len(lst2) > 0:
# ...and the first number in `lst1` is greater than the first number
# in `lst2`: append the first value of `lst2` to the `ret` list, but
# only when the `ret` list does not yet contain that value
# and remove the first number from `lst2`
if lst1[0] > lst2[0]:
append_if_not_exists(ret, lst2[0])
lst2 = lst2[1:]
# ...and the first number in `lst1` is smaller than the first number
# in `lst2`: append the first value of `lst1` to the `ret` list, only
# if the `ret` list does not yet contain that value.
# Remove the first number from `lst1`
elif lst1[0] < lst2[0]:
append_if_not_exists(ret, lst1[0])
lst1 = lst1[1:]
# ...and both lists have the same first number: append the first
# value of the lists to the `ret` list, if that list does not yet
# contain the value.
# Remove the first number from both lists
elif lst1[0] == lst2[0]:
append_if_not_exists(ret, lst1[0])
lst1 = lst1[1:]
lst2 = lst2[1:]
# Else, when one or both lists have run out of elements...
# ...if `lst1` is empty, append each value of `lst2` to the `ret` list,
# but only if it is not yet in the `ret` list.
if len(lst1) == 0:
for i in lst2:
append_if_not_exists(ret, i)
# ... if `lst2` is empty, append each value of `lst1` to the `ret` list,
# but only if it is not yet in that list.
if len(lst2) == 0:
for i in lst1:
append_if_not_exists(ret, i)
# Return the merged list
return ret
def merge(lst1, lst2):
"""Merges two sorted lists `lst1` and `lst2`
Returns a sorted list where `lst1` and `lst2` are merged and deduplicated
"""
# # Loop invariant
# @require Both lists are already sorted
# @require `ret` is empty list that will contain the values when the lists
# have been merged.
# @return The two lists merged into one, sorted and deduped
# @loop:
# @while Unprocessed entries in one or both lists
# @do:
# Take the first unprocessed entry from both lists and compare them
# Add the smallest entry to the merged list (if not yet present)
# and mark that entry as processed.
# Check if both lists are sorted (function sorted() in sortedList.py)
# Return false if the lists are not sorted
if not sortedList.sorted(lst1) or not sortedList.sorted(lst2):
return False
# The variable that will hold the merged list.
ret = []
# While both lists still have elements...
while len(lst1) > 0 and len(lst2) > 0:
# ...and the first number in `lst1` is greater than the first number
# in `lst2`: append the first value of `lst2` to the `ret` list, but
# only when the `ret` list does not yet contain that value
# and remove the first number from `lst2`
if lst1[0] > lst2[0]:
append_if_not_exists(ret, lst2[0])
lst2 = lst2[1:]
# ...and the first number in `lst1` is smaller than the first number
# in `lst2`: append the first value of `lst1` to the `ret` list, only
# if the `ret` list does not yet contain that value.
# Remove the first number from `lst1`
elif lst1[0] < lst2[0]:
append_if_not_exists(ret, lst1[0])
lst1 = lst1[1:]
# ...and both lists have the same first number: append the first
# value of the lists to the `ret` list, if that list does not yet
# contain the value.
# Remove the first number from both lists
elif lst1[0] == lst2[0]:
append_if_not_exists(ret, lst1[0])
lst1 = lst1[1:]
lst2 = lst2[1:]
# Else, when one or both lists have run out of elements...
# ...if `lst1` is empty, append each value of `lst2` to the `ret` list,
# but only if it is not yet in the `ret` list.
if len(lst1) == 0:
for i in lst2:
append_if_not_exists(ret, i)
# ... if `lst2` is empty, append each value of `lst1` to the `ret` list,
# but only if it is not yet in that list.
if len(lst2) == 0:
for i in lst1:
append_if_not_exists(ret, i)
# Return the merged list
return ret
