Comparing c# array to itself

Question

I'm trying to solve whats probably an easy task, but I'm extremely new to this and don't quite have my head around working with arrays in a complex fashion. I'm trying to figure out if two inputs each corresponding numbers sum to the same number (for example with 123 and 321, 1+3 2+2 and 1+3 all equal 4).

The code I have so far has broken down each input into arrays, and I can sum those arrays into a third array, but I cant figure out how to check it with itself. Should I even bother with the 3rd array, and just figure out how to check the sums of the array in a loop?

public static void Main()
{
    Console.Write("\n\n"); //begin user input
    Console.Write("Check whether each cooresponding digit in two intigers sum to the same number or not:\n");
    Console.Write("-------------------------------------------");
    Console.Write("\n\n");
    Console.Write("Input 1st number then hit enter: ");
    string int1 = (Console.ReadLine());//user input 1


    Console.Write("Input 2nd number: ");
    string int2 = (Console.ReadLine());//user input 2

    int[] numbers = new int[int1.ToString().Length]; //changing user inputs to strings for array
    int[] numbers2 = new int[int2.ToString().Length];
    for (int i = 0; i < numbers.Length; i++)
    {
        numbers[i] = int.Parse(int1.Substring(i, 1));//populating arrays
        numbers2[i] = int.Parse(int2.Substring(i, 1));
    }


    int[] numbers3 = new int[numbers.Length];

    for (int i = 0; i < numbers.Length; i++)
    {
        numbers3[i] = (numbers[i] + numbers2[i]);
    }
}

}

Aydin · Accepted Answer · 2018-08-09 03:43:36Z

2

You can create the collections on the fly...

bool isEqual = Console.ReadLine()
                      .ToCharArray()
                      .Select(i => Convert.ToInt32(i.ToString()))
                      .Zip(Console.ReadLine()
                                  .ToCharArray()
                                  .Select(i => Convert.ToInt32(i.ToString())),
                           (i, j) => new
                           {
                               First = i,
                               Second = j,
                               Total = i + j
                           })
                      .GroupBy(x => x.Total)
                      .Count() == 1;

The output will equal true if all elements add up to the same value...

Test cases:

Should succeed

12345
54321

Should fail

12345
55432

To understand the above query, lets break it up into sections.

// Here I'm just converting a string to an IEnumerable<int>, a collection of integers basically
IEnumerable<int> ints1 = Console.ReadLine()
                                .ToCharArray()
                                .Select(i => Convert.ToInt32(i.ToString()));

IEnumerable<int> ints2 = Console.ReadLine()
                                .ToCharArray()
                                .Select(i => Convert.ToInt32(i.ToString()));

// Zip brings together two arrays and iterates through both at the same time.
// I used an anonymous object to store the original values as well as the calculated ones
var zippedArrays = ints1.Zip(ints2, (i, j) => new
                                    {
                                        First = i,    // original value from ints1
                                        Second = j,   // original values from ints2
                                        Total = i + j // calculated value ints1[x] + ints2[x]
                                    });



// if the totals are [4,4,4], the method below will get rid of the duplicates.
// if the totals are [4,3,5], every element in that array would be returned
// if the totals are [4,4,5], only [4,5] would be returned.
var distinctByTotal = zippedArrays.GroupBy(x => x.Total);

// So what does this tell us? if the returned collection has a total count of 1 item,
// it means that every item in the collection must have had the same total sum
// So we can say that every element is equal if the response of our method == 1.

bool isEqual = distinctByTotal.Count() == 1;

edited Aug 9, 2018 at 3:43

answered Aug 9, 2018 at 2:39

Aydin

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3 Comments

ba7399 Over a year ago

this is super useful for me, I see zip used alot and only get explanations like this every so often. thanks!

mjwills Over a year ago

Great solution. Also consider github.com/morelinq/MoreLINQ/blob/master/MoreLinq/ZipLongest.cs if the two enumerables may be different lengths.

Aydin Over a year ago

@mjwills thank you for sharing that, it did run through my mind, the thought of what if the two collections are different lengths, but chose to not pursue it... I like what they did with it!

MineR · Accepted Answer · 2018-08-09 04:36:57Z

0

You're 99% of the way there already. Just lose the third array and check each individual sum in your final loop.

bool isOK = numbers.Length = numbers2.Length && numbers.Length > 0;
if(isOK)
{
    int expectedSum = numbers[0] + numbers2[0];
    for (int i = 1; i < numbers.Length; i++)
    {
        var sum = (numbers[i] + numbers2[i]);
        if(sum != expectedSum)
        {
            isOK = false;
            break;
        }
    }
}
Console.WriteLine(isOk ? "Good job." : "You got some learning to do.");

answered Aug 9, 2018 at 4:36

MineR

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