Question

List<Int32> dansConList = new List<Int32>();
dansConList[0] = 1;
dansConList[1] = 2;
dansConList[2] = 3;

List<Int32> dansRandomList = new List<Int32>();
dansRandomList[0] = 1;
dansRandomList[1] = 2;
dansRandomList[2] = 4;

I need a method that, when evaluating the above lists, will return false for dansRandomList and true for dansConList based on the fact dansConList has a consecutive number sequence in it’s values, and dansRandomList does not (missing the value 3).

Using LINQ is preferable, if possible.

What I’ve Tried:

• For the sake of achieving the end result, I have used a for loop and compare with ‘i’ (loop counter) to evaluate the values, but as mentioned above I’d like to use LINQ for this.

Answer 1

One-liner, only iterates until the first non-consecutive element:

bool isConsecutive = !myIntList.Select((i,j) => i-j).Distinct().Skip(1).Any();

Update: a couple examples of how this works:

Input is { 5, 6, 7, 8 }
Select yields { (5-0=)5, (6-1=)5, (7-2=)5, (8-3=)5 }
Distinct yields { 5, (5 not distinct, 5 not distinct, 5 not distinct) }
Skip yields { (5 skipped, nothing left) }
Any returns false

Input is { 1, 2, 6, 7 }
Select yields { (1-0=)1, (2-1=)1, (6-2=)4, (7-3=)4 } *
Distinct yields { 1, (1 not distinct,) 4, (4 not distinct) } *
Skip yields { (1 skipped,) 4 }
Any returns true

* The Select will not yield the second 4 and the Distinct will not check it, as the Any will stop after finding the first 4.