Add doctests for fractional knapsack (TheAlgorithms#10891)

* Add doctests for fractional knapsack

* Update greedy_methods/fractional_knapsack.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Run doctests

* Update greedy_methods/fractional_knapsack.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update greedy_methods/fractional_knapsack.py

---------

Co-authored-by: Christian Clauss <cclauss@me.com>

Author: Hardvan

greedy_methods/fractional_knapsack.py

@@ -6,6 +6,30 @@ def frac_knapsack(vl, wt, w, n):
     """
     >>> frac_knapsack([60, 100, 120], [10, 20, 30], 50, 3)
     240.0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], 10, 4)
+    105.0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], 8, 4)
+    95.0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6], 8, 4)
+    60.0
+    >>> frac_knapsack([10, 40, 30], [5, 4, 6, 3], 8, 4)
+    60.0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], 0, 4)
+    0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], 8, 0)
+    95.0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], -8, 4)
+    0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], 8, -4)
+    95.0
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], 800, 4)
+    130
+    >>> frac_knapsack([10, 40, 30, 50], [5, 4, 6, 3], 8, 400)
+    95.0
+    >>> frac_knapsack("ABCD", [5, 4, 6, 3], 8, 400)
+    Traceback (most recent call last):
+        ...
+    TypeError: unsupported operand type(s) for /: 'str' and 'int'
     """
 
     r = sorted(zip(vl, wt), key=lambda x: x[0] / x[1], reverse=True)