Python/searches/interpolation_search.py

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2017-10-15 16:11:10 +00:00
"""
This is pure python implementation of interpolation search algorithm
"""
from __future__ import print_function
try:
raw_input # Python 2
except NameError:
raw_input = input # Python 3
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def interpolation_search(sorted_collection, item):
"""Pure implementation of interpolation search algorithm in Python
Be careful collection must be sorted, otherwise result will be
unpredictable
:param sorted_collection: some sorted collection with comparable items
:param item: item value to search
:return: index of found item or None if item is not found
"""
left = 0
right = len(sorted_collection) - 1
while left <= right:
point = left + ((item - sorted_collection[left]) * (right - left)) // (sorted_collection[right] - sorted_collection[left])
#out of range check
if point<0 or point>=len(sorted_collection):
return None
current_item = sorted_collection[point]
if current_item == item:
return point
else:
if item < current_item:
right = point - 1
else:
left = point + 1
return None
def interpolation_search_by_recursion(sorted_collection, item, left, right):
"""Pure implementation of interpolation search algorithm in Python by recursion
Be careful collection must be sorted, otherwise result will be
unpredictable
First recursion should be started with left=0 and right=(len(sorted_collection)-1)
:param sorted_collection: some sorted collection with comparable items
:param item: item value to search
:return: index of found item or None if item is not found
"""
point = left + ((item - sorted_collection[left]) * (right - left)) // (sorted_collection[right] - sorted_collection[left])
#out of range check
if point<0 or point>=len(sorted_collection):
return None
if sorted_collection[point] == item:
return point
elif sorted_collection[point] > item:
return interpolation_search_by_recursion(sorted_collection, item, left, point-1)
else:
return interpolation_search_by_recursion(sorted_collection, item, point+1, right)
def __assert_sorted(collection):
"""Check if collection is sorted, if not - raises :py:class:`ValueError`
:param collection: collection
:return: True if collection is sorted
:raise: :py:class:`ValueError` if collection is not sorted
Examples:
>>> __assert_sorted([0, 1, 2, 4])
True
>>> __assert_sorted([10, -1, 5])
Traceback (most recent call last):
...
ValueError: Collection must be sorted
"""
if collection != sorted(collection):
raise ValueError('Collection must be sorted')
return True
if __name__ == '__main__':
import sys
user_input = raw_input('Enter numbers separated by comma:\n').strip()
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collection = [int(item) for item in user_input.split(',')]
try:
__assert_sorted(collection)
except ValueError:
sys.exit('Sequence must be sorted to apply interpolation search')
target_input = raw_input('Enter a single number to be found in the list:\n')
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target = int(target_input)
result = interpolation_search(collection, target)
if result is not None:
print('{} found at positions: {}'.format(target, result))
else:
print('Not found')