added interpolation search

Author: sarbajitsaha

Diff for: searches/interpolation_search.py

@@ -0,0 +1,102 @@
+"""
+This is pure python implementation of interpolation search algorithm
+"""
+from __future__ import print_function
+import bisect
+
+
+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
+    # For python 2.x and 3.x compatibility: 3.x has no raw_input builtin
+    # otherwise 2.x's input builtin function is too "smart"
+    if sys.version_info.major < 3:
+        input_function = raw_input
+    else:
+        input_function = input
+
+    user_input = input_function('Enter numbers separated by comma:\n')
+    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 = input_function(
+        'Enter a single number to be found in the list:\n'
+    )
+    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')