This is my quick sort code, the partition function works well, but I got a problem while calling the recursion. The pos changes every time it starts the function and then the list limits are change as well. How to fix that?
def partition(lst, start, end):
pos=0
if len(lst)<2:
return
for i in range(len(lst[start:end])):
if lst[i] < lst[end]:
lst[i],lst[pos]=lst[pos],lst[i]
pos+=1
elif i==(len(lst[start:end])-1):
lst[end],lst[pos]=lst[pos],lst[end]
return pos
def quick_sort_recursive(lst, start, end):
pos=partition(lst, start, end)
if start<=pos<=end :
quick_sort_recursive(lst, start, pos-1)
quick_sort_recursive(lst, pos+1, end)
else:
return lst
There are numerous problems in your code, here are some fixes just to make it work:
def partition(lst, start, end):
pos = start # condition was obsolete, loop won't
# simply run for empty range
for i in range(start, end): # i must be between start and end-1
if lst[i] < lst[end]: # in your version it always goes from 0
lst[i],lst[pos] = lst[pos],lst[i]
pos += 1
lst[pos],lst[end] = lst[end],lst[pos] # you forgot to put the pivot
# back in its place
return pos
def quick_sort_recursive(lst, start, end):
if start < end: # this is enough to end recursion
pos = partition(lst, start, end)
quick_sort_recursive(lst, start, pos - 1)
quick_sort_recursive(lst, pos + 1, end)
# you don't need to return the list
# it's modified in place
Example:
example = [3,45,1,2,34]
quick_sort_recursive(example, 0, len(example) - 1)
print example
Gives:
python test.py
[1, 2, 3, 34, 45]