// ConsoleApplication7.cpp : main project file.

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;

string merge(string a, string b)
{
	if (a.length() == 0)
		return b;
	if (b.length() == 0)
		return a;
	if (a[0] < b[0])
		return a[0] + merge(a.substr(1, a.length()-1), b);
	else
		return b[0] + merge(a, b.substr(1, b.length()-1));
}

string dedup(string in)
{
	if (in.length() < 2)
		return in;
	if (in[0] == in[1])
		return in[1] + dedup(in.substr(2, in.length() - 2));
	else
		return in[0] + dedup(in.substr(1, in.length() -1));
}

int count(string s)
{
	if (s.length() == 0)
		return 0;
	if (s[0] == 'A')
		return 1 + count(s.substr(1,s.length()-1));
	else
		return count(s.substr(1,s.length()-1));
}
int sum(int a, int b)
{
	if (a > b)
		return 0;
	else
		return a + sum(a+1, b);
}

int div10(int num)
{
	if (num < 10)
		return 0;
	else
		return 1 + div10(num-10);
}


int main(array<System::String ^> ^args)
{
	// DO ANY THREE OF THESE.
	// ONLY DO THREE OF THESE.
	// THERE ARE FIVE.  YOU CAN SKIP TWO!


	// Make a recursive function that returns the sum of the
	// integers from A .. B.
	cout << sum(1,3) << " -- sum(1,3) Should be 1+2+3 = 6" << endl;
	cout << sum(5,10) << " -- sum(5,10) Should be 5+6+7+8+9+10 = 45" << endl;
	cout << sum(-2,2) << " -- sum(-2,2) Should be -2 + -1 + 0 + 1 + 2 = 0" << endl;

	cout << endl << endl;


	// Make a function that divided by 10.
	// You may not use the "/" operator.
	// The argument will be non-negative.
	// You must round down.
	cout << div10(0)   << " -- div10(0) = 0" << endl;
	cout << div10(34)  << " -- div10(34) = 3" << endl;
	cout << div10(117) << " -- div10(117) = 17" << endl;
	cout << div10(9)   << " -- div10(9) = 0" << endl;

	cout << endl << endl;


	// Make a recusive function that counts the number of 'A's in the string.
	cout << count("A") << " -- count(\"A\") -- Should be 1" << endl;
	cout << count("") << " -- count(\"\") -- Should be 0" << endl;
	cout << count("ABBA") << " -- count(\"ABBA\") -- Should be 2" << endl;
	cout << count("A large dog AA") << " -- count(\"A large dog AA\") -- Should be 3" << endl;
	cout << count("recusion is fun") << " -- count(\"recursion is fun\") -- Should be 0" << endl;

	cout << endl << endl;

	// Make a recursive method that eliminates the second letter of duplicate letters 
	// that are next to each other.
	cout << dedup("AB") << " -- dedup(\"AB\") -- Should produce AB" << endl;
	cout << dedup("") << " -- dedup(\"\") -- Should produce the empty string" << endl;
	cout << dedup("mississippi") << " -- dedup(\"mississippi\") -- Should produce misisipi" << endl;
	cout << dedup("ABBA") << " -- dedup(\"ABBA\") -- Should produce ABA" << endl;

	cout << endl << endl;
	
	// Merge two strings that are ordered alphabetically.
	// The results should also be alphabetic.
	cout << merge("abd", "cef") << " -- merge(\"abe\", \"cef\") should be abcdef " << endl;
	cout << merge("", "")       << " -- merge(\"\", \"\") -- should be the empty string." << endl;
	cout << merge("xy", "abc")  << " -- merge(\"xy\", \"abc\") -- should be abcxy." << endl;
	cout << merge("abxy", "dd") << " -- merge(\"abxy\", \"dd\") -- should be abddxy." << endl;
    
        system("pause");
}