Left or Right rotation in-place using Python

• Input: [1, 2, 3, 4, 5, 6, 7, 8, 9]
• Output Left shift by 4: [5, 6, 7, 8, 9, 1, 2, 3, 4]
• Output Right shift by 5: [5, 6, 7, 8, 9, 1, 2, 3, 4]

 

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• Interviewer: Left shift by 4 and Right shift by 5

data = [1, 2, 3, 4, 5, 6, 7, 8, 9]
left_shifts = 4
right_shifts = 5

left = data[left_shifts:]+ data[:left_shifts]
right = data[-right_shifts:]+ data[:-right_shifts]

print("left: ", left)
print("right: ", right)

 

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• Interviewer: Left shift by 4 in-place, without slicing

data = [1, 2, 3, 4, 5, 6, 7, 8, 9]
shifts = 4

shifts = shifts % (len(data))

# Reverse entire array
for i in range(len(data)//2):
    tmp = data[i]
    data[i] = data[-i-1]
    data[-i-1] = tmp

shifts = len(data)-shifts

# Reverse first k items
for i in range(shifts//2):
    tmp = data[i]
    data[i] = data[shifts-i-1]
    data[shifts-i-1] = tmp

# Reverse the rest
for i in range((len(data)-shifts)//2):
    tmp = data[shifts+i]
    data[shifts+i] = data[-i-1]
    data[-i-1] = tmp

print(data)

 

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• Interviewer: Right shift by 5 in-place, without slicing

data = [1, 2, 3, 4, 5, 6, 7, 8, 9]
shifts = 5

shifts = shifts % (len(data))

# Reverse entire array
for i in range(len(data)//2):
    tmp = data[i]
    data[i] = data[-i-1]
    data[-i-1] = tmp

# Reverse first k items
for i in range(shifts//2):
    tmp = data[i]
    data[i] = data[shifts-i-1]
    data[shifts-i-1] = tmp

# Reverse the rest
for i in range((len(data)-shifts)//2):
    tmp = data[shifts+i]
    data[shifts+i] = data[-i-1]
    data[-i-1] = tmp

print(data)

 

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