Conditional Probability Table

Estimate $P(A\mid B)P(A\backslash mid\; B)$ from paired binary observations: among the cases where $BB$ happened, the fraction where $AA$ also happened.

Implement solve(A, B).

Returns. Return a float. Any non-zero entry counts as true. If $BB$ never occurs the conditional probability is undefined and the function returns 0.0.

Examples

Example 1

Input:

solve([1, 0, 1, 1], [1, 1, 1, 0])

Output:

0.666667

Example 2

Input:

solve([1, 1], [0, 0])

Output:

0.0