def partition(arr, left, right):
"""
Its task is do the partition (the array bw the left-right range both inclusive) and return the pivot_index
1. Select a pivot index
Randomized for better performance [average O(n log n)] , else O(n2)
2. partition the array over that pivot_index
3. return the pivot_index
"""
randomize_pivot(arr, left, right)
# NOTE : Right now our actual_pivot is at index right
future_correct_pivot_index = left # let say
actual_pivot_value = arr[right]
while left < right: # going till the adjacent element of right
if arr[left] < actual_pivot_value:
# arr[left], arr[future_correct_pivot_index] = arr[future_correct_pivot_index], arr[left]
swap_array_elements(arr, left, future_correct_pivot_index)
future_correct_pivot_index += 1
left += 1
# swapping the actual_pivot to its correct_index
arr[future_correct_pivot_index], arr[right] = arr[right], arr[
future_correct_pivot_index]
return future_correct_pivot_index
def reverse_recursively_helper(arr, left, right):
if left >= right:
return # traversal complete
# swap the two extreme elements
swap_array_elements(arr, left,
right) # arr[left], arr[right] = arr[right], arr[left]
reverse_recursively_helper(arr, left + 1, right - 1)
def reverse_iterative(arr):
left, right = 0, len(arr) - 1
while left < right:
swap_array_elements(
arr, left, right) # arr[left], arr[right] = arr[right], arr[left]
left += 1
right -= 1
return arr
def partition_around_0(A, left, right):
pivot_value = 0
future_correct_pivot_index = left
# as our pivot element external and not in array
while left <= right: # Going till the last element and not just to 2nd last Notice
if A[left] < pivot_value:
# A[left], A[future_correct_pivot_index] = A[future_correct_pivot_index], A[left]
swap_array_elements(arr, left, future_correct_pivot_index)
future_correct_pivot_index += 1
left += 1
def two_pointer(arr):
left = 0
right = len(arr) - 1
while left < right:
if arr[left] < 0: # -ve
left += 1 # go right
if arr[right] >= 0: # +ve
right -= 1 # go left
if not (not (arr[left] >= 0)
or not (arr[right] < 0)): # left is -Ve and right is +Ve
swap_array_elements(array, left,
right) # A[left], A[right] = A[right], A[left]
left += 1
right -= 1
def push_non_negative_unique_integers_to_correct_index(arr):
n = len(arr)
for i in range(0, n):
while arr[i] < n and i != arr[i]: # The condition arr[i]<n, will handle the out of bound scenarios
swap_array_elements(arr, i, arr[i]) # Note : arr[i] , arr[arr[i]] = arr[arr[i]] , arr[i] Will Not Work!