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Dictionaries, Hash Tables and Sets

  1. Write a program that counts in a given array of double values the number of occurrences of each value. Use Dictionary<TKey,TValue>.

    Example: array = {3, 4, 4, -2.5, 3, 3, 4, 3, -2.5}

    • -2.5 -> 2 times
    • 3 -> 4 times
    • 4 -> 3 times

  • Write a program that extracts from a given sequence of strings all elements that present in it odd number of times.

    Example: {C#, SQL, PHP, PHP, SQL, SQL } -> {C#, SQL}

  • Write a program that counts how many times each word from given text file words.txt appears in it. The character casing differences should be ignored. The result words should be ordered by their number of occurrences in the text.

    Example: This is the TEXT. Text, text, text – THIS TEXT! Is this the text?

    • is -> 2
    • the -> 2
    • this -> 3
    • text -> 6

  • Implement the data structure "hash table" in a class HashTable<K, T>. Keep the data in array of lists of key-value pairs LinkedList<KeyValuePair<K, T>>[] with initial capacity of 16. When the hash table load runs over 75%, perform resizing to 2 times larger capacity. Implement the following methods and properties: Add(key, value), Find(key) -> value, Remove(key), Count, Clear(), this[], Keys. Try to make the hash table to support iterating over its elements with foreach.

  • Implement the data structure "set" in a class HashedSet<T> using your class HashTable<K,T> to hold the elements. Implement all standard set operations like Add(T), Find(T), Remove(T), Count, Clear(), union and intersect.

  • * A text file phones.txt holds information about people, their town and phone number:

    Name Town Phone
    Mimi Shmatkata Plovdiv 0888 12 34 56
    Kireto Varna 052 23 45 67
    Daniela Ivanova Petrova Karnobat 0899 999 888
    Bat Gancho Sofia 02 946 946 946

    Duplicates can occur in people names, towns and phone numbers. Write a program to read the phones file and execute a sequence of commands given in the file commands.txt:

    • find(name) – display all matching records by given name (first, middle, last or nickname)
    • find(name, town) – display all matching records by given name and town