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# 10.28 (Partition of a list) Write the following function that partitions the list using the
# first element, called a pivot:
# def partition(lst):
# After the partition, the elements in the list are rearranged so that all the elements
# before the pivot are less than or equal to the pivot and the element after
# the pivot are greater than the pivot. The function also returns the index where
# the pivot is located in the new list. For example, suppose the list is [5, 2, 9, 3,
# 6, 8]. After the partition, the list becomes [3, 2, 5, 9, 6, 8]. Implement the
# function in a way that takes len(lst) comparisons. Write a test program
# that prompts the user to enter a list and displays the list after the partition.
def main():
s = input("Enter a list: ")
items = s.split() # Extracts items from the string
list = [eval(x) for x in items] # Convert items to numbers
partition(list)
print("After the partition, the list is ", end="")
for e in list:
print(e, end=" ")
def partition(list):
pivot = list[0] # Choose the first element as the pivot
low = 1 # Index for forward search
high = len(list) - 1 # Index for backward search
while high > low:
# Search forward from left
while low <= high and list[low] <= pivot:
low += 1
# Search backward from right
while low <= high and list[high] > pivot:
high -= 1
# Swap two elements in the list
if high > low:
list[high], list[low] = list[low], list[high]
while high > 1 and list[high] >= pivot:
high -= 1
# Swap pivot with list[high]
if pivot > list[high]:
list[0] = list[high]
list[high] = pivot
main()
