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Language/Type: C# Dictionary collections

Write a method named LastNamesByAge that accepts three parameters: 1) a SortedDictionary where each key is a person's full name (a string) and the associated value is that person's age (an integer); 2) an integer for a minimum age; and 3) an integer for a max age. Your method should return a new dictionary with information about people with ages between the min and max, inclusive.

In your result map, each key is an integer age, and the value for that key is a string with the last names of all people at that age, separated by "and" if there is more than one person of that age. The order of names for a given age should be in the order they occurred in the parameter map. Include only ages between the min and max inclusive, where there is at least one person of that age in the parameter map. If the dictionary passed is empty, or if there are no people in the dictionary between the min/max ages, return an empty dictionary.

Some names are in the format "first last" such as "Jane Doe". But a name could have more tokens, such as "Oscar de la Hoya", or could contain just a single token, such as "Cher". For example, if a dictionary named ages stores the following key/value pairs:

{{"Allison L. Smith", 18}, {"Benson Kai Lim", 48}, {"David L Shaw", 20}, {"Erik Thomas Jones", 20},
 {"Galen Wood", 15}, {"Madonna", 25}, {"Helene Q. Martin", 40}, {"Janette Siu", 18},
 {"Jessica K. Miller", 35}, {"Marty Douglas Stepp", 35}, {"Paul Beame", 28}, {"Sara de la Pizza", 15},
 {"Stuart T. Reges", 98}, {"Tyler Rigs", 6}, {"Prince", 20}}

The call of LastNamesByAge(ages, 16, 25) should return the following dictionary:

{{18, "Smith and Siu"}, {20, "Shaw and Jones and Prince"}, {25, "Madonna"}}

For the same map, the call of LastNamesByAge(ages, 20, 40) should return the following dictionary:

{{20, "Shaw and Jones and Prince"}, {25, "Young"}, {28, "Beame"}, {35, "Miller and Stepp"}, {40, "Martin"}}

Constraints: Obey the following restrictions in your solution.

  • You will need to construct a dictionary to store your results, but you may not use any other structures (arrays, lists, etc.) as auxiliary storage. (You can have as many simple variables as you like.)
  • You should not modify the contents of the dictionary passed to your method.
    Declare your method in such a way that any caller can be sure that this will not happen.
  • Your solution should run in no worse than O(N log N) time, where N is the number of pairs in the dictionary.
Method: Write a C# method as described, not a complete program or class.

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