add two files to pull request

Iterative and recursive versions of Interpolation Search.
Details in comments.

interpolation_iter.py

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+# Python program to implement interpolation search
+#  using iteration approach
+def interpolationSearch(arr, n, x):
+
+	# Find indexes of two corners
+	low = 0
+	high = (n - 1)
+
+	# Since array is sorted, an element present
+	# in array must be in range defined by corner
+	while low <= high and x >= arr[low] and x <= arr[high]:
+		if low == high:
+			if arr[low] == x:
+				return low;
+			return -1;
+
+		# Probing the position with keeping
+		# uniform distribution in mind.
+		pos = int(low + (((float(high - low)/( arr[high] - arr[low])) * (x - arr[low]))))
+
+		# Condition of target found
+		if arr[pos] == x:
+			return pos
+
+		# If x is larger, x is in upper part
+		if arr[pos] < x:
+			low = pos + 1;
+
+		# If x is smaller, x is in lower part
+		else:
+			high = pos - 1;
+	
+	return -1
+
+# Main function
+if __name__ == "__main__":
+	# Array of items on whighch search will
+	# be conducted.
+	arr = [10, 12, 13, 16, 18, 19, 20, 21,
+		22, 23, 24, 33, 35, 42, 47]
+	n = len(arr)
+
+	x = 18 # Element to be searched
+	index = interpolationSearch(arr, n, x)
+
+	# If element was found
+	if index != -1:
+		print ("Element found at index",index)
+	else:
+		print ("Element not found")

interpolation_recurse.py

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+# Python program to implement
+# interpolation search  with recursion
+# If x is present in arr[0..n-1], then
+# returns index of it, else returns -1.
+# Time complexity is O(log(log(n)) in
+# average case. O(n) in the worst case.
+
+
+def interpolationSearch(arr, lo, hi, x):
+
+	# Since array is sorted, an element present
+	# in array must be in range defined by corner
+	if (lo <= hi and x >= arr[lo] and x <= arr[hi]):
+
+		# Probing the position while keeping
+		# uniform distribution in mind.
+		pos = lo + ((hi - lo) // (arr[hi] - arr[lo]) *
+					(x - arr[lo]))
+
+		# Condition of target found
+		if arr[pos] == x:
+			return pos
+
+		# If x is larger, x is in right subarray
+		if arr[pos] < x:
+			return interpolationSearch(arr, pos + 1,hi, x)
+
+		# If x is smaller, x is in left subarray
+		if arr[pos] > x:
+			return interpolationSearch(arr, lo,pos - 1, x)
+	return -1
+
+# Driver code
+
+
+# Array of items in which
+# search will be conducted
+arr = [10, 12, 13, 16, 18, 19, 20,
+	21, 22, 23, 24, 33, 35, 42, 47]
+n = len(arr)
+
+# Element to be searched
+x = 18
+index = interpolationSearch(arr, 0, n - 1, x)
+
+if index != -1:
+	print("Element found at index", index)
+else:
+	print("Element not found")
+
+