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## Learning Opportunities

This puzzle can be solved using the following concepts. Practice using these concepts and improve your skills.

## Goal

Calculate the equivalent resistance of a circuit containing only resistors.

A resistor is a component used in electrical circuits. A resistor is quantified by its Resistance, which is measured in Ohms. We are interested in knowing the total resistance of a circuit of only resistors. There are two key definitions needed to determine the resistance of multiple resistors.

1. Series

The resistance of resistors in a line is equivalent to the sum of the resistance of those resistors.

    ---[R_1]---[R_2]---

Resistors in series will be noted with parentheses ( R_1 R_2 R_3 ... and so on ).

The resistance of a series arrangement is: R_eq = R_1 + R_2 + R_3 + ... and so on, where R_eq is the equivalent resistance of the series arrangement.

2. Parallel

The resistance of resistors in branching paths of the circuit is equal to 1 over the sum of 1 over the resistance of each branching path.

       +---[R_1]---+       |           |    ---+           +---       |           |       +---[R_2]---+

Resistors in parallel will be noted with brackets [ R_1 R_2 R_3 ... and so on ].

The resistance of resistors in parallel is R_eq = 1/(1/R_1 + 1/R_2 + 1/R_3 + 1/... and so on).

A branch can be treated as a single resistor by determining its equivalent resistance.

Example:

N = 3
A 24B 8C 48[ ( A B ) [ C A ] ]

This will look something like this:

       +---[C]---+       |         |    +--+         +--+    |  |         |  |    |  +---[A]---+  |    |               |    +---[A]---[B]---+    |               |    +---[Battery]---+

[ ( A B ) [ C A ] ] => [ 24+8 1/(1/48+1/24) ] => [ 32 16 ] => 1/(1/32+1/16) => 32/3 => 10.666... => 10.7
Input
Line 1: An integer N for the number of unique resistors present in the circuit
Next N lines: A space separated name and the integer resistance R of a resistor
Last line: A space separated combination of parentheses, brackets, and names of resistors
Output
The equivalent resistance expressed as a float rounded to the nearest 0.1 Ohms.
Constraints
0 < N < 10
0 < R < 100
Example
Input
2
A 20
B 10
( A B )
Output
30.0

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