From ed63c9edb75ac0edca0b10510ff7578c03860b20 Mon Sep 17 00:00:00 2001
From: Anurag Bhandari <bhandari2003anurag@gmail.com>
Date: Sun, 2 Oct 2022 22:48:00 +0530
Subject: [PATCH] added interpolation search

---
 interpolation_search.py | 139 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 interpolation_search.py

diff --git a/interpolation_search.py b/interpolation_search.py
new file mode 100644
index 0000000..8292e61
--- /dev/null
+++ b/interpolation_search.py
@@ -0,0 +1,139 @@
+"""
+This is pure Python implementation of interpolation search algorithm
+"""
+
+
+def interpolation_search(sorted_collection, item):
+    """Pure implementation of interpolation search algorithm in Python
+    Be careful collection must be ascending sorted, otherwise result will be
+    unpredictable
+    :param sorted_collection: some ascending 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:
+        # avoid divided by 0 during interpolation
+        if sorted_collection[left] == sorted_collection[right]:
+            if sorted_collection[left] == item:
+                return left
+            else:
+                return None
+
+        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 point < left:
+                right = left
+                left = point
+            elif point > right:
+                left = right
+                right = 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 ascending sorted, otherwise result will be
+    unpredictable
+    First recursion should be started with left=0 and right=(len(sorted_collection)-1)
+    :param sorted_collection: some ascending sorted collection with comparable items
+    :param item: item value to search
+    :return: index of found item or None if item is not found
+    """
+
+    # avoid divided by 0 during interpolation
+    if sorted_collection[left] == sorted_collection[right]:
+        if sorted_collection[left] == item:
+            return left
+        else:
+            return None
+
+    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 point < left:
+        return interpolation_search_by_recursion(sorted_collection, item, point, left)
+    elif point > right:
+        return interpolation_search_by_recursion(sorted_collection, item, right, left)
+    else:
+        if 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 ascending sorted, if not - raises :py:class:`ValueError`
+    :param collection: collection
+    :return: True if collection is ascending sorted
+    :raise: :py:class:`ValueError` if collection is not ascending sorted
+    Examples:
+    >>> __assert_sorted([0, 1, 2, 4])
+    True
+    >>> __assert_sorted([10, -1, 5])
+    Traceback (most recent call last):
+    ...
+    ValueError: Collection must be ascending sorted
+    """
+    if collection != sorted(collection):
+        raise ValueError("Collection must be ascending sorted")
+    return True
+
+
+if __name__ == "__main__":
+    import sys
+
+    """
+        user_input = input('Enter numbers separated by comma:\n').strip()
+    collection = [int(item) for item in user_input.split(',')]
+    try:
+        __assert_sorted(collection)
+    except ValueError:
+        sys.exit('Sequence must be ascending sorted to apply interpolation search')
+    target_input = input('Enter a single number to be found in the list:\n')
+    target = int(target_input)
+        """
+
+    debug = 0
+    if debug == 1:
+        collection = [10, 30, 40, 45, 50, 66, 77, 93]
+        try:
+            __assert_sorted(collection)
+        except ValueError:
+            sys.exit("Sequence must be ascending sorted to apply interpolation search")
+        target = 67
+
+    result = interpolation_search(collection, target)
+    if result is not None:
+        print(f"{target} found at positions: {result}")
+    else:
+        print("Not found")
\ No newline at end of file