pigeonhole sorting in python (TheAlgorithms#364)

* pigeonhole sorting in python

* variable name update in pigeonhole_sort.py

* Add doctest

Author: SHAKTISINGH2323

sorts/pigeonhole_sort.py

@@ -0,0 +1,44 @@
+# Python program to implement Pigeonhole Sorting in python
+
+# Algorithm for the pigeonhole sorting
+
+
+def pigeonhole_sort(a):
+    """
+    >>> a = [8, 3, 2, 7, 4, 6, 8]
+    >>> b = sorted(a)  # a nondestructive sort
+    >>> pigeonhole_sort(a)  # a distructive sort
+    >>> a == b
+    True
+    """
+    # size of range of values in the list (ie, number of pigeonholes we need)
+
+    min_val = min(a)  # min() finds the minimum value
+    max_val = max(a)  # max() finds the maximum value
+
+    size = max_val - min_val + 1  # size is difference of max and min values plus one
+
+    # list of pigeonholes of size equal to the variable size
+    holes = [0] * size
+
+    # Populate the pigeonholes.
+    for x in a:
+        assert isinstance(x, int), "integers only please"
+        holes[x - min_val] += 1
+
+    # Putting the elements back into the array in an order.
+    i = 0
+    for count in range(size):
+        while holes[count] > 0:
+            holes[count] -= 1
+            a[i] = count + min_val
+            i += 1
+
+
+def main():
+    pigeonhole_sort([8, 3, 2, 7, 4, 6, 8])
+    print("Sorted order is: ", " ", join(a))
+
+
+if __name__ == "__main__":
+    main()