```
'''
This is a type of divide and conquer algorithm which divides the search space into
3 parts and finds the target value based on the property of the array or list
(usually monotonic property).
Time Complexity : O(log3 N)
Space Complexity : O(1)
'''
from __future__ import print_function
import sys
try:
raw_input # Python 2
except NameError:
raw_input = input # Python 3
# This is the precision for this function which can be altered.
# It is recommended for users to keep this number greater than or equal to 10.
precision = 10
# This is the linear search that will occur after the search space has become smaller.
def lin_search(left, right, A, target):
for i in range(left, right+1):
if(A[i] == target):
return i
# This is the iterative method of the ternary search algorithm.
def ite_ternary_search(A, target):
left = 0
right = len(A) - 1;
while(True):
if(left<right):
if(right-left < precision):
return lin_search(left,right,A,target)
oneThird = (left+right)/3+1;
twoThird = 2*(left+right)/3+1;
if(A[oneThird] == target):
return oneThird
elif(A[twoThird] == target):
return twoThird
elif(target < A[oneThird]):
right = oneThird-1
elif(A[twoThird] < target):
left = twoThird+1
else:
left = oneThird+1
right = twoThird-1
else:
return None
# This is the recursive method of the ternary search algorithm.
def rec_ternary_search(left, right, A, target):
if(left<right):
if(right-left < precision):
return lin_search(left,right,A,target)
oneThird = (left+right)/3+1;
twoThird = 2*(left+right)/3+1;
if(A[oneThird] == target):
return oneThird
elif(A[twoThird] == target):
return twoThird
elif(target < A[oneThird]):
return rec_ternary_search(left, oneThird-1, A, target)
elif(A[twoThird] < target):
return rec_ternary_search(twoThird+1, right, A, target)
else:
return rec_ternary_search(oneThird+1, twoThird-1, A, target)
else:
return None
# This function is to check if the array is sorted.
def __assert_sorted(collection):
if collection != sorted(collection):
raise ValueError('Collection must be sorted')
return True
if __name__ == '__main__':
user_input = raw_input('Enter numbers separated by coma:\n').strip()
collection = [int(item) for item in user_input.split(',')]
try:
__assert_sorted(collection)
except ValueError:
sys.exit('Sequence must be sorted to apply the ternary search')
target_input = raw_input('Enter a single number to be found in the list:\n')
target = int(target_input)
result1 = ite_ternary_search(collection, target)
result2 = rec_ternary_search(0, len(collection)-1, collection, target)
if result2 is not None:
print('Iterative search: {} found at positions: {}'.format(target, result1))
print('Recursive search: {} found at positions: {}'.format(target, result2))
else:
print('Not found')
```