Is it possible to express this code in LINQ?

Question

I'm reading a C# book for beginners, and in every end of the chapter, there are exercises to be answered based on the lessons tackled.

One of those exercises goes this way: (not the exact wordings)

Write a program that will accept an int as the array length, and the values for the array.
Then will print:
"0" if the array is not sorted in ascending way.
"1" if it is sorted. And,
"2" if it is sorted, but there are duplicates.

Example:

// Sorted
Input: 1, 2, 3, 5
Print: 1

// Not sorted
Input: 2, 1, 3, 6
Print: 0

// Sorted, but with duplicates
Input: 2, 2, 3, 7
Print: 2

I don't know if my logic here is absolute, but somehow it is working,
and I done it in my way using this code:

int arrayLength = 0;
int prev, next;
int sortStatus = 1;

Console.Write("Input array Length: ");
arrayLength = Convert.ToInt32(Console.ReadLine());
int[] ar = new int[arrayLength];

for (int x = 0; x < arrayLength; x++)
{
    Console.Write("Input {0} value: ", (x+1).ToString());
    ar[x] = Convert.ToInt32(Console.ReadLine());
}

for (int x = 0; x < ar.Length-1; x++)
{
    prev = (int)ar[x];
    next = (int)ar[x + 1];

    if (next < prev)
        sortStatus = 0;
    if (next == prev)
        sortStatus = 2;
}

Console.Write(sortStatus.ToString());
Console.Read();

Is it possible to express this in LINQ? How?

Answer 1

if (ar.SequenceEqual(ar.OrderBy(x => x)))
{
    if (ar.Distinct().Count() == ar.Length)
        return 1;
    else
        return 2;
}
else 
{
    return 0;
}

Answer 2

A pure LINQ alternative ... (for academic interest only (but probably still faster than the accepted answer!)

var input = new int[] { 1, 2, 3, 4, 5 };

var output = input.Zip(input.Skip(1), (a, b) => new {a=a, b=b})
                .Aggregate(1, (status, x) => status == 0 ? 0 : ((x.a > x.b ? 0 : (x.a == x.b ? 2 : status))));

Answer 3

As a note, your expressed non-LINQ logic has a flaw.

if (next < prev) 
    sortStatus = 0; 
if (next == prev) 
    sortStatus = 2; 

Your rule says that the array must be sorted ascending but have duplicates in order to get an output of 2. However, your logic will return 2 for { 1, 9, 7, 7 }.

Another way to write your code might be the following. (This is not using LINQ, but this is too long to post as a comment to your question.)

static int EvaluateArray(int[] array)
{
    int? lastItem = null;
    bool match = false;
    foreach (int item in array)
    {
        if (item < lastItem)
            return 0;
        else if (item == lastItem)
            match = true;

        lastItem = item;
    }

    if (match)
        return 2;

    return 1;
}

In this method, we will early-return as soon as we have an item less than the previous item. Otherwise, we will set a boolean if we come across a matching value. At the end of the loop, we know the array is sorted ascending. The only thing left is check if there was a match.

Answer 4

Untested.

IEnumerable<int> signs = 
  from i in Enumerable.Range(0, ar.Length).Skip(1)
  select ar[i-1].CompareTo(ar[i]);

int result =
  signs.Any(sign => sign < 0) ? 0 :
  signs.All(sign => 0 < sign) ? 1 :
  2;

---

Also untested:

int minSign = !ar.Skip(1).Any() ? 1 :
(
  from i in Enumerable.Range(0, ar.Length).Skip(1)
  select ar[i-1].CompareTo(ar[i])
).TakeWhile(x => 0 <= x).Min();

int result =
  minSign < 0 ? 0 :
  0 < minSign ? 1 :
  2;