(Sorted?) Python Question

Question

Write the following function that returns True if the list is already sorted in increasing order:

def isSorted(lst):

Write a test program that prompts the user to enter a list of numbers separated by a space in one line and displays whether the list is sorted or not. Don’t use the Python list sort method in this program. Here is a sample run:

Sample Run 1

Enter list: 1 1 3 4 4 5 7 9 10 30 11

The list is not sorted

Sample Run 2

Enter list: 1 1 3 4 4 5 7 9 10 30

The list is already sorted

Answer 1

Hello, so I started with grabbing the indices of the actual numbers, since the input asks the user to include whitespace between the numbers. In the second step, I wanted to ensure there wouldn't essentially be an out of range issue so I checked to see if the last number in the list was less than the second to last, and if so, return 'Not sorted'. The final step loops through the list of indices and maps it to the original list to check if the number in the current iteration is greater than the number after it (the i + 2 is there to account for whitespace in the original list) and returns a message based on whether or not its true. Further checks could be done in the event that the user accidentally inputs a double space instead of just one or if they start the list off with a space instead of a number. Maybe a list.replace() or re.sub() would be appropriate but for simplicity's sake, I omitted those.

def is_sorted(x):

ind = [i for i,j in enumerate(x) if j.isnumeric()]

if x[ind[-1]] < x[ind[-2]]:

return x, 'Not sorted'

else:

for i in ind:

if x[i] > x[i+2]:

return x, 'The list is not sorted'

return x, 'The list is sorted'

if __name__ == '__main__':

listx = input('Please enter a list of numbers separated by a space: ')

is_sorted(listx)

Answer 2

Hey Richard you can split the input into a list and then loop through and check current and previous values as in:

# Check if list is sorted

def isSorted(inputList):

listLen = len(inputList)

if listLen < 2 :

return True

i = 1

while i < len(inputList):

if int(inputList[i]) < int(inputList[i-1]):

return False

i = i + 1

return True

# get input and split into a list

def getAndChecklist(input):

inputList = input.split()

print("Entered List", inputList)

if isSorted(inputList) :

print("The list is already sorted")

else :

print("The list is not sorted")

# Sample Run 1

getAndChecklist("1 1 3 4 4 5 7 9 10 30 11")

# Sample Run 2

getAndChecklist("1 1 3 4 4 5 7 9 10 30")