# Compute the Resistance of a 4 Band Color Coded Resistor

Resistors commonly have color coded bands that are used to identify their resistance in Ohms. In this challenge we'll only consider the normal 4-band, tan, axial-lead resistors. We'll express them as:

xyzt


Where x is the first band for the first significant figure, y is the second band for the second significant figure, z the third band for the multiplier, and t is the fourth band for the tolerance.

Each of xyzt represents a letter that abbreviates the color of the band:

K = Black
N = Brown
R = Red
O = Orange
Y = Yellow
G = Green
B = Blue
V = Violet
A = Gray
W = White
g = Gold
s = Silver
_ = None


So, for example, NKOg is some particular resistor.

The resistance can be calculated with the help of this table:

As the table suggests:

• x and y can be any letters except g, s, and _.
• z can be anything except _.
• We'll restrict t to only be g, s, or _.

The resistance is 10 * x + y times the z multiplier, to a tolerance of the t percentage.

For example, to calculate the resistance of NKOg, we see that:

1. N means Brown for 1.
2. K means Black for 0.
3. O means Orange for 103.
4. g means Gold for ±5%.

So the resistance is (10*1 + 0)*10^310000 Ω ±5%.

# Challenge

Write a program or function that takes in a 4 character string of the form xyzt and prints or returns the resistance in the form [resistance] Ω ±[tolerance]%.

• The resistor may be "upside-down", i.e. in the reverse order tzyx. For example, both NKOg and gOKN should produce 10000 Ω ±5%.
• The resistance is always in plain ohms, never kilohms, megohms, etc.
• Ω may be replaced with ohms, e.g. 10000 ohms ±5%.
• ± may be replaced with +/-, e.g. 10000 Ω +/-5%.
• Having trailing zeros to the right of a decimal point is fine. (e.g. 10000.0 Ω +/-5%)
• You can assume input is always valid (x and y never gs_; z never _; t only gs_).
• All 10×10×12×3 = 3600 possible resistors (2×3600 possible inputs) need to be supported even if some color band combinations aren't produced in real life.

The shortest code in bytes wins.

# Examples

1. gOKN10000 ohms +/-5%
2. KKR_0 Ω +/-20%
3. ggKN1 ohms ±5%
4. ggGO3.5 Ω ±5%
5. ssGO0.350 Ω ±10%
6. GOOs53000 ohms +/-10%
7. YAK_48.0 ohms +/-20%
8. _WAV78000000000 Ω ±20%
9. gBBB66000000.000 ohms ±5%
10. _RYR2400.00 ohms ±20%

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# CJam, 595856 50 bytes

r_W%e>"sgKNROYGBVAW"f#2f-~A*+A@#*" Ω ±"@[KA5]='%


Try it online in the CJam interpreter.

# CJam, 5351 50 bytes

" Ω ±"l_W%e<)iB%5*F-'%@"gKNROYGBVAW"f#:(2/'e*s~o


(Thanks to @user23013 for a byte)

I started out in Python, but

eval("%d%de%d"%tuple("gKNROYGBVAW".find(x)-1for x in L))


was too expensive...

• :(2/'e*s~ saves the [. May 26 '15 at 5:35
• @user23013 Ah thanks, I've been trying a bunch of ways of inserting the e where it's necessary, but I never thought of / and * May 26 '15 at 5:39

## Python 3, 130 114 bytes

def f(v):
a,b,c,d=["_sgKNROYGBVAW".index(x)-3for x in v[::(1,-1)[v[0]in'sg_']]]
return "%s Ω ±%s%%"%((10*a+b)*10**c,2.5*2**-d)


edit: @Sp3000 points out that the ordering can be better detected with min(v,v[::-1]) rather than v[::(1,-1)[v[0]in'sg_']] (saving 10 bytes), not check the index of _ and remove some unnecessary whitespace.

def f(v):a,b,c,d=["sgKNROYGBVAW".find(x)-2for x in min(v,v[::-1])];return"%s Ω ±%s%%"%((10*a+b)*10**c,2.5*2**-d)

• Thanks - I realised about concatenating the lines, but I missed the trick of using min() to detect the correct ordering - nice. May 26 '15 at 15:04

# Perl, 93 bytes

#!perl -lp
ord>90and$_=reverse;s/./-3+index zsgKNROYGBVAW,$&/ge;$_=s/..\K/e/*$_." Ω ±"./.$/*5*$&."%"


# Haskell, 135 132 130 bytes

r y|y<"["=p[k|j<-y,(c,k)<-zip"_ sgKNROYGBVAW"[-4..],c==j]
r y=r.reverse$y p[a,b,c,d]=show((a*10+b)*10**c)++" Ω ±"++show(-5*d)++"%"  Explanation: r y|y<"["= If first letter of argument is a capital p[..] Call p on the list created [k| Make a list of all k j<-y Draw character j from input ,(c,k)<- With (c,k) being a pair from zip A list of pairs of corresponding elements from the lists: "_ sgKNROYGBVAW" The space at 2nd position is to match '_' with -4, but 's' with -2 [-4..] An infinite list starting at -4 ,c==j] Only use element k if j equals the character c r y=r.reverse$y       If first call fails, call again with reversed argument.

p[a,b,c,d]=           Assign the first four elements of the argument to a,b,c,d respectively.
show                  Turn (number) into string
10**c                 10 to the power of c
++                    Concatenate strings
-5*d                  This works for the tolerance because '_' makes d=-4


Thanks to nimi, I shaved off another 2 bytes.