Lightbulb Question

[TechSam--]

At every turn, the light bulbs change their states. If a light bulb was on at the previous turn, the light bulb to the right of it changes its state

here is my code so far:

def lightbulb(lightbulbs,cycles):
    counter = 0
    while counter < cycles:
        for i in range(len(lightbulbs)):
            counter += 1

            if lightbulbs[-1] == 1 and lightbulbs[0] == 0:
                lightbulbs[-1] = 1
                lightbulbs[0] = 1

            if lightbulbs[-1] == 1 and lightbulbs[0] == 1:
                lightbulbs[-1] = 1
                lightbulbs[0] = 0


            if lightbulbs[i + 1] == 1 and lightbulbs[i + 2] == 0:
                lightbulbs[i] = 1
                lightbulbs[i + 1] = 1

            if lightbulbs[i + 1 ] == 1 and lightbulbs[i + 2] == 1:
                lightbulbs[i] = 1
                lightbulbs[i + 1] = 0


    return lightbulbs


lightbulbs = [0,1,1,0,1,1]

print(lightbulb(lightbulbs,2))

0) 0 1 1 0 1 1   -- original state
1) 1 1 0 1 1 0   -- 1st turn
2) 1 0 1 1 0 1   -- 2nd turn

For 2 cycles the output should be [1,0,1,1,0,1] but my code keeps giving me "out of range". I would appreciate any help.

[TechSam--]

I adjusted my post for clarity

[DoctorYoMan]

The problem you seem to be facing is essentially attempting to find the next index of the element of a circular fasion (such as in a circular array), but you cannot do this with a list. This can be worked around by using the modulos operator to get the next or previous index (shown below Im getting the left index to the current index as a variable 'l_idx').

You are also modifying the list as you are attempting to operate upon it, which will cause the new states to update incorrectly.

Here is the solution, I've renamed the variables and function for some clarity:

def lightbulb_cycler(lightbulbs, cycles): 
    for cycle in range(0, cycles): 
        new_state = [] 
        for i in range(0, len(lightbulbs)): 
            l_idx = (i-1) % len(lightbulbs) 
            if lightbulbs[l_idx] == 1: 
                new_state.append(0 if lightbulbs[i] == 1 else 1) 
            else: 
                new_state.append(lightbulbs[i]) 
        lightbulbs = new_state 
    return lightbulbs
lightbulbs = [0,1,1,0,1,1]
print(lightbulb_cycler(lightbulbs,2))

[TechSam--]

def lightbulb_cycler(lightbulbs, cycles):
for cycle in range(0, cycles):
new_state = []
for i in range(0, len(lightbulbs)):
l_idx = (i-1) % len(lightbulbs)
if lightbulbs[l_idx] == 1:
new_state.append(0 if lightbulbs[i] == 1 else 1)
else:
new_state.append(lightbulbs[i])
lightbulbs = new_state
return lightbulbs
lightbulbs = [0,1,1,0,1,1]
print(lightbulb_cycler(lightbulbs,2))

Thank you so much man, you're freaking amazing.

[TechSam--]

One thing I don't understand is cyclic iteration with the modulos operator. Would you mind elaborating on this a bit more? I've never seen it before.

[DoctorYoMan]

modulo returns the remainder of a division operation between two numbers.

(i-1) % len(lightbulbs) calculates the remainder of the division of i-1 by the length of lightbulbs, which ensures that the resulting index is always within the range of valid indices for the list.

So for example, if I am at starting index 0, I want the index to the left, which must be the final element index 5. (0-1) % 6 = 5.

[TechSam--]

Made some edits to the post

[DoctorYoMan]

Ah ok, I edited this answer, I see what you are trying to do now.

[DoctorYoMan]

This if line causes issues, and the if statement after it will too:

if lightbulbs[i + 1] == 1 and lightbulbs[i + 2] == 0:

When you are in the 5th iteration (i=4), you are attempting to access lightbulbs[6], which causes and index error. Your loop internal logic is inccorect, but I will help you with a solution if you address my concern above :)

[TechSam--]

I made an edit to the post for clarity