Recruiting test

Test assignment

Thank you for participating in our recruiting test. This will be a C++ programming test!

Task Description

interval_map<K,V> is a data structure that associates keys of type K with values of type V. It is designed to be used efficiently in situations where intervals of consecutive keys are associated with the same value. Your task is to implement the assign member function of this data structure, which is outlined below.

interval_map<K, V> is implemented on top of std::map. For more information on std::map, you may refer to cppreference.com.

Each key-value-pair (k,v) in interval_map<K,V>::m_map means that the value v is associated with all keys from k (including) to the next key (excluding) in m_map. The member interval_map<K,V>::m_valBegin holds the value that is associated with all keys less than the first key in m_map.

Example: Let M be an instance of interval_map<int,char> where

• M.m_valBegin=='A',
• M.m_map=={ (1,'B'), (3,'A') },

Then M represents the mapping

• ...
• -2 -> 'A'
• -1 -> 'A'
• 0 -> 'A'
• 1 -> 'B'
• 2 -> 'B'
• 3 -> 'A'
• 4 -> 'A'
• 5 -> 'A'
• ...

The representation in the std::map must be canonical, that is, consecutive map entries must not contain the same value: ..., (3,'A'), (5,'A'), ... is not allowed. Likewise, the first entry in m_map must not contain the same value as m_valBegin. Initially, the whole range of K is associated with a given initial value, passed to the constructor of the interval_map<K,V> data structure.

Key type K

• besides being copyable and assignable, is less-than comparable via operator<, and
• does not implement any other operations, in particular no equality comparison or arithmetic operators.

Value type V

• besides being copyable and assignable, is equality-comparable via operator==, and
• does not implement any other operations.

#include <map>
template<typename K, typename V>
class interval_map {
	friend void IntervalMapTest();
	V m_valBegin;
	std::map<K,V> m_map;
public:
	// constructor associates whole range of K with val
	interval_map(V const& val)
	: m_valBegin(val)
	{}

	// Assign value val to interval [keyBegin, keyEnd).
	// Overwrite previous values in this interval.
	// Conforming to the C++ Standard Library conventions, the interval
	// includes keyBegin, but excludes keyEnd.
	// If !( keyBegin < keyEnd ), this designates an empty interval,
	// and assign must do nothing.
	void assign( K const& keyBegin, K const& keyEnd, V const& val ) {

	}

	// look-up of the value associated with key
	V const& operator[]( K const& key ) const {
		auto it=m_map.upper_bound(key);
		if(it==m_map.begin()) {
			return m_valBegin;
		} else {
			return (--it)->second;
		}
	}
};

// Many solutions we receive are incorrect. Consider using a randomized test
// to discover the cases that your implementation does not handle correctly.
// We recommend to implement a test function that tests the functionality of
// the interval_map, for example using a map of int intervals to char.

Your task is to implement the function assign. Your implementation is graded by the following criteria in this order:

• Type requirements are met: You must adhere to the specification of the key and value type given above.
• Correctness: Your program should produce a working interval_map with the behavior described above. In particular, pay attention to the validity of iterators. It is illegal to dereference end iterators. Consider using a checking STL implementation such as the one shipped with Visual C++ or GCC.
• Canonicity: The representation in m_map must be canonical.

• Running time: Imagine your implementation is part of a library, so it should be big-O optimal. In addition:

  • Do not make big-O more operations on K and V than necessary because you do not know how fast operations on K/V are; remember that constructions, destructions and assignments are operations as well.
  • Do not make more than one operation of amortized O(log N), in contrast to O(1), running time, where N is the number of elements in m_map.
  • Otherwise favor simplicity over minor speed improvements.

You should not take longer than 9 hours, but you may of course be faster. Do not rush, we would not give you this assignment if it were trivial.

When you are done, please complete the form and click Compile. You can improve and compile solutions as often as you like.

Compile

Further instructions will be given once your code compiles correctly.