Sort algorithm to sort a list of strings (C#)

Question

I'm doing this assignment for uni and the requirement is that I use any sorting algorithm to sort a List in alphabetical order (case insensitive). Basically say if the list contains some strings for example, "a" "C" "b" "1" and "3" it will sort it to either "1" "3" "a" "b" "C" or "a" "b" "C" "1" "3" I know how to sort an array of integers (code below using exchange sort) but how do I use a list of strings instead? How to modify the code below to sort a list of strings alphabetically while still maintaining the principles of exchange sort (in this case)?

Note: I am not allowed to use List<string>.Sort() or some other simple code.

        // sort a vector of type int using exchange sort
        public void ExchangeSort(int[] array)
        {
            int pass, i, n = array.Length;
            int temp;
            // make n-1 passes through the data 
            for (pass = 0; pass < n - 1; pass++)
            {
                // locate least of array[pass] ... array[n - 1]  
                // at array[pass] 
                for (i = pass + 1; i < n; i++)
                {
                    if (array[i] < array[pass])
                    {
                        temp = array[pass];
                        array[pass] = array[i];
                        array[i] = temp;
                    }
                }
            }
        }

To start with, what happens when you change the type of array and temp to string[] and string respectively? — Koterpillar
– Koterpillar, Commented Mar 17, 2013 at 6:14
@Koterpillar The main problem is you can't compare strings using <. here is the error: www3.picturepush.com/photo/a/12433536/1024/Anonymous/… — Steve Way
– Steve Way, Commented Mar 17, 2013 at 6:22

cHao · Accepted Answer · 2013-03-17 07:01:57Z

3

You'll probably need to compare the strings char by char.

In pseudocode:

for each I from 0 to (shorter string's length - 1):
    if left[I] is a letter and right[I] isn't (or vice versa):
        the string that has a letter at [I] is "less"
        done
    else:
        ("true" here means ignore case)
        (you could also say `StringComparison.InvariantCultureIgnoreCase`, but eh)
        result = String.Compare(left, I, right[I], I, 1, true)
        if result < 0
            left is "less"
        else if result > 0
            right is "less"
        else
            (both strings are equal so far)
            next I

(if you're here, the strings are "equal" up to this point)

if both strings have the same length:
    they're equal
else:
    the longer string is "greater"

edited Mar 17, 2013 at 7:01

answered Mar 17, 2013 at 6:26

cHao

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2 Comments

Steve Way Over a year ago

could you write the full code? I'm a complete beginner so I'm not really getting your pseudo-code.

cHao Over a year ago

Part of the point of the assignment is to get you writing some code on your own. :) Let me know what part needs clarifying, and i'll explain.

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