C#•2y ago

❔ Verify Uniqueness in an Array

Does anyone know how to determine if an array contain unique names in an array without using previously defined methods. I have worked on this for days and finally just had to submit the homework without figuring it out. The instructions: "Given an array of string, names, verify that each name is unique meaning that none of the names are duplicated within the array. If the array is unique, return true; otherwise, return false." My code:

public static bool Test4(string [] names)
        {
                  bool unique = false;
                  for (int i = 0; i < names.Length; i++)
                  {
                        for(int j = 1; j < i; j++)
                        {
                              if (names[i] != names[j] && names[j] != names[i])
                              {
                                    unique = true;

                              }
                              else if (names[i] == names[j] && names[j] == names[i])
                              {
                                    unique = false;
                              }
                        }
                  }
                  return unique;
        }

public static bool Test4(string [] names)
        {
                  bool unique = false;
                  for (int i = 0; i < names.Length; i++)
                  {
                        for(int j = 1; j < i; j++)
                        {
                              if (names[i] != names[j] && names[j] != names[i])
                              {
                                    unique = true;

                              }
                              else if (names[i] == names[j] && names[j] == names[i])
                              {
                                    unique = false;
                              }
                        }
                  }
                  return unique;
        }

7 Replies

JakenVeina•2y ago

would "without using previously defined methods" include not using HashSet<T>? cause that'd be the easiest way

public static bool AreValuesUnique(IEnumerable<string> values)
{
    var uniqueValues = new HashSet<string>();
    foreach(var value in values)
    {
        if(!uniqueValues.Add(value))
            return false;
    }

    return true;
}

public static bool AreValuesUnique(IEnumerable<string> values)
{
    var uniqueValues = new HashSet<string>();
    foreach(var value in values)
    {
        if(!uniqueValues.Add(value))
            return false;
    }

    return true;
}

otherwise

public static bool AreValuesUnique(IEnumerable<string> values)
{
    var uniqueValues = new List<string>();
    foreach(var value in values)
    {
        if (uniqueValues.Contains(value))
            return false;
        uniqueValues.Add(value);
    }

    return true;
}

public static bool AreValuesUnique(IEnumerable<string> values)
{
    var uniqueValues = new List<string>();
    foreach(var value in values)
    {
        if (uniqueValues.Contains(value))
            return false;
        uniqueValues.Add(value);
    }

    return true;
}

TravestyOfCode•2y ago

Take a simple example to test with: { "John", "Amy", "Bob" }. Your loops should be checking : "John" and "Amy", "John" and "Bob", and "Amy" and "Bob". There's not a need to check both "John" and "Bob" and then "Bob" and "John". If a = b, then b = a so it's duplicate work. Also the moment you find a duplicate, you can stop checking as you just need to return a true or false. For example in { "John", "John", "Amy", "Bob", "Alice", "Amy" } once you determine that John is duplicated, you know that the array is not unique and never can be, so there isn't a need to check for "Amy" and "Amy".

Jimmacle•2y ago

sounds like they expect you to use nested loops and return early, so your solution is pretty close to what it should be

𝔉𝓮𝓵𝓲𝓬𝓲𝓪 𝓗𝓪𝓰𝓰𝓪𝓻𝓭OP•2y ago

For some reason my professor had me set it up that way. That is what my professor said however I haven't been able to figure it out.

TravestyOfCode•2y ago

So the first loop, i is going through all of the strings in array, and the inner nested loop is going through all of the strings in the array starting after the one your first loop is looking at. When i gets to the end, it doesn't need to check the last string against the last string, though. i will need to be the second to last element because j is going to be the last element.

TravestyOfCode•2y ago

When I first started learning programming, I would draw out each step to visualize what was happening like this:

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Verify Uniqueness in an Array