PROBLEM STATEMENT
A big box contains marbles of one or more colors. You're given a vector <int> colors, each element 
of which denotes the number of marbles there are of a particular color. You draw n marbles 
randomly from the box, leaving each marble outside the box after taking it. Return the probability 
that all marbles drawn will be the same color.

DEFINITION
Class:DrawingMarbles
Method:sameColor
Parameters:vector <int>, int
Returns:double
Method signature:double sameColor(vector <int> colors, int n)


NOTES
-Every time we draw a marble, all marbles in the box are equally likely to be chosen.
-A return value with either an absolute or relative error of less than 1.0E-9 is considered correct.


CONSTRAINTS
-colors will contain between 1 and 50 elements, inclusive.
-Each element of colors will be between 1 and 50, inclusive.
-n will be between 1 and the sum of all elements of colors, inclusive.


EXAMPLES

0)
{ 13 }
8

Returns: 1.0

All the marbles are the same color, so obviously all drawn marbles will be the same color too.

1)
{ 5, 7 }
1

Returns: 1.0



2)
{ 5, 6, 7 }
2

Returns: 0.3006535947712418

The probability that the first drawn marble will be of the color 0 is 5 / 18 (there are 5 marbles 
of color 0 out of 18). If the first drawn marble is of the color 0, then the probability that the 
second drawn marble will be of the color 0 is 4 / 17 (there are 4 marbles of color 0 left out of 
17). So the probability that both drawn marbles will be of the color 0 is (5 / 18) * (4 / 17) = 
0.0653594771... . Similarly, the probability that both drawn marbles will be of the color 1 is (6 
/ 18) * (5 / 17) = 0.0980392156..., and that both drawn marbles will be of the color 2 is (7 / 18) 
* (6 / 17) = 0.1372549019... . The answer is the sum of these 3 probabilities.

3)
{ 12, 2, 34, 13, 17 }
4

Returns: 0.035028830818304504



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