Arrays: Left Rotation Discussions |

9 years ago+ 42 comments

Based on current index (i), you need to generate new index. For example: let's say array = [1, 2, 3, 4] and k = 2, then after 2 left rotation it should be [3, 4, 1, 2] => 3 4 1 2 (space separated string output)

Now let's walk through my algorithm:

# Initial assignments:
  # array = [1, 2, 3, 4]
  # length_of_array = array.length = 4
  # no_of_left_rotation = k = 2
  # new_arr = Arra.new(length_of_array)
	# new_arr: [nil, nil, nil, nil]

# NOTE:
  # length_of_array.times do |i|
    # is equivalent to 
  # for(i = 0; i < length_of_array; i++)

# Algorithm to calculate new index and update new array for each index (i):
  # new_index = (i + no_of_left_rotation) % length_of_array
  # new_arr[i] = array[new_index]

# LOOP1:
  # i = 0
  # new_index = (0 + 2) % 4 = 2
  # new_arr[i = 0] = array[new_index = 2] = 3
  # new_arr: [3, nil, nil, nil]

# LOOP2:
  # i = 1
  # new_index = (1 + 2) % 4 = 3
  # new_arr[i = 1] = array[new_index = 3] = 4
  # new_arr: [3, 4, nil, nil]

# LOOP3:
  # i = 2
  # new_index = (2 + 2) % 4 = 0
  # new_arr[i = 2] = array[new_index = 0] = 1
  # new_arr: [3, 4, 1, nil]

# LOOP4:
  # i = 3
  # new_index = (3 + 2) % 4 = 1
  # new_arr[i = 3] = array[new_index = 1] = 2
  # new_arr: [3, 4, 1, 2]

# After final loop our new roated array is [3, 4, 1, 2]
# You can return the output: 
  # new_arr.join(' ') => 3 4 1 2

Hope that's clear.

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