CODEWITHSUNDEEP
c#listlinq
Abhi.Net
Abhi.Net

Reputation: 772

Elegant way to compare each value in 2 sorted integer lists using Linq

I am trying to find the best way to compare values in 2 integer lists and return the list as soon as I find value in one list is bigger than the other

[1,2,3] and [1,2,4]

return second list [1,2] are equal but 4 in second list is greater than 3 in first list

[4,2,3] and [1,5,6]

return first list because the 4 in first list is greater than 1 in second list. No need to check other elements.

Now I can use a loop here but I am sure there is a better way using Linq.

Upvotes: 1

Views: 163

Answers (3)

Vivek Nuna
Vivek Nuna

Reputation: 1

You can try this simple solution, I am considering that list can be null and of different length.

public static List<int> GetBiggerList(List<int> ls1, List<int> ls2)
{
    if (ls1 == null)
        return ls2;
    if (ls2 == null)
        return ls2;

    int length = Math.Min(ls1.Count, ls2.Count);

    for (int i = 0; i < length; i++)
    {
        if (ls1[i] > ls2[i])
            return ls1;
        if (ls2[i] > ls2[i])
            return ls2;
    }

    if (ls1.Count > ls2.Count)
        return ls1;

    return ls2;
}

Upvotes: 1

Ian Mercer
Ian Mercer

Reputation: 39277

Assuming the two lists are the same length, you can find the first element that's not equal using LINQ:

    var firstDifference = array1.Zip(array2, (a,b) => (a,b))
         .SkipWhile(x => x.a == x.b).FirstOrDefault();

After that it's easy to handle the three cases: default, a<b, a>b.

Edit: To handle these three cases you could do:

    int firstDifference = array1.Zip(array2, (a,b) => (a,b))
         .SkipWhile(x => x.a == x.b)
         .Select(x => x.a.CompareTo(x.b))    // -1 or +1
         .FirstOrDefault();                  // 0 if no elements

This gives 0, -1 or +1 because default(int) is 0.

Upvotes: 2

user12031933
user12031933

Reputation:

Without Linq

static int[] Compare(int[] list1, int[] list2)
{
  if ( list1 == null && list2 == null ) return null;
  if ( list1 == null ) return list2;
  if ( list2 == null ) return list1;
  for ( int index = 0; index < list1.Length && index < list2.Length; index++ )
  {
    int compareValue = list1[index].CompareTo(list2[index]);
    if (compareValue == 0) continue;
    if (compareValue > 0) return list1;
    return list2;
  }
  int compareLength = list1.Length.CompareTo(list2.Length);
  if ( compareLength == 0 ) return null;
  if ( compareLength > 0 ) return list1;
  return list2;
}

Test

var list1 = new int[] { 1, 2, 3 };
var list2 = new int[] { 1, 2, 4 };

var list3 = new int[] { 4, 2, 3 };
var list4 = new int[] { 1, 5, 6 };

var list5 = new int[] { 1, 2 };

Action<int[]> print = list =>
{
    Console.WriteLine(list == null ? "Same" : string.Join(",", list));
};

print(Compare(list1, list2));
print(Compare(list3, list4));
print(Compare(list1, list5));
print(Compare(list5, list1));
print(Compare(list1, list1));
print(Compare(null, list1));
print(Compare(list1, null));
print(Compare(new int[0], list1));
print(Compare(list1, new int[0]));

Output

1,2,4
4,2,3
1,2,3
1,2,3
Same
1,2,3
1,2,3
1,2,3
1,2,3

Upvotes: 0

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