Here is a simple merge sort algorithm I tried to implement in python. I tried to do this without using left and right parameters which are found elsewhere, only using slices.
from math import floor
def merge(A, B):
"""Mearges the two sorted lists A and B"""
merged = []
i, j = 0, 0
while i < len(A) and j < len(B):
if A[i] <= B[j]:
merged.append(A[i])
i = 1
else:
merged.append(B[j])
j = 1
if j == len(B):
merged.extend(A[i:])
elif i == len(A):
merged.extend(B[j:])
return merged
def merge_sort(A):
if len(A) == 1:
return A
m = floor(len(A) / 2)
half1 = A[0:m]
half2 = A[m:]
A = merge_sort(half1)
B = merge_sort(half2)
R = merge(A, B)
return R
def main():
C = [6, 7, 2]
print(merge_sort(C))
exit()
if __name__ == "__main__":
main()
And it worked fine. But when I tried
A = merge_sort(A[0:m])
B = merge_sort(A[m:])
instead of using the variables half1
and half2
in merge_sort
function, I got this:
Traceback (most recent call last):
File "/home/aayush/PyProgs/mrg_sort.py", line 44, in <module>
main()
File "/home/aayush/PyProgs/mrg_sort.py", line 40, in main
print(merge_sort(C))
File "/home/aayush/PyProgs/mrg_sort.py", line 32, in merge_sort
B = merge_sort(A[m:])
File "/home/aayush/PyProgs/mrg_sort.py", line 31, in merge_sort
A = merge_sort(A[0:m])
File "/home/aayush/PyProgs/mrg_sort.py", line 31, in merge_sort
A = merge_sort(A[0:m])
File "/home/aayush/PyProgs/mrg_sort.py", line 31, in merge_sort
A = merge_sort(A[0:m])
[Previous line repeated 993 more times]
File "/home/aayush/PyProgs/mrg_sort.py", line 25, in merge_sort
if len(A) == 1:
RecursionError: maximum recursion depth exceeded while calling a Python object
Please tell me what I have done wrong.
CodePudding user response:
you just need to keep check of variable naming since here A is updated and you are using that list data not the orignal one
def merge_sort(A):
if len(A) == 1:
return A
m = floor(len(A) / 2)
c = merge_sort(A[0:m])
B = merge_sort(A[m:])
R = merge(c, B)
return R
CodePudding user response:
Have you try with smaller data ?
Try :
import sys sys.setrecursionlimit(10000)
Then retry If algorithm not ended, you have an infinite loop