ROUGE

Given a candidate and a reference (both str) pieces, complete the rouge2 function that calculates the $\text{ROUGE-2}_{\text{F1}}$ score. Return the resulting score, rounded to the third digit.

Tip: A reminder of the necessary equations:

$\text{ROUGE-2}_{\text{recall}} = \frac{\text{bigram cand. } \cap \text{ bigram ref.}}{|\text{bigram ref.}|}$

$\text{ROUGE-2}_{\text{precision}}= \frac{\text{bigram cand. } \cap \text{ bigram ref.}}{|\text{bigram cand.}|}$

$\text{ROUGE-2}_{\text{F1}}=2*\frac{\text{recall}*\text{precision}}{\text{recall} + \text{precision}}$