psf/black code formatting (#1421)

* added sol3.py for problem_20

* added sol4.py for problem_06

* ran `black .` on `\Python`

dynamic_programming/abbreviation.py

@@ -11,6 +11,7 @@ a=daBcd and b="ABC"
 daBcd -> capitalize a and c(dABCd) -> remove d (ABC)
 """
 
+
 def abbr(a, b):
     """
     >>> abbr("daBcd", "ABC")

dynamic_programming/fibonacci.py

@@ -58,7 +58,7 @@ if __name__ == "__main__":
                 print("\nInvalid input, please try again.")
     except NameError:
         print("\n********* Invalid input, good bye!! ************\n")
-        
+
     import doctest
 
     doctest.testmod()

dynamic_programming/fractional_knapsack.py

@@ -20,6 +20,7 @@ def fracKnapsack(vl, wt, W, n):
         else sum(vl[:k])
     )
 
+
 if __name__ == "__main__":
     import doctest
 

dynamic_programming/longest_common_subsequence.py

@@ -76,7 +76,7 @@ if __name__ == "__main__":
     expected_subseq = "GTAB"
 
     ln, subseq = longest_common_subsequence(a, b)
-##    print("len =", ln, ", sub-sequence =", subseq)
+    ##    print("len =", ln, ", sub-sequence =", subseq)
     import doctest
 
     doctest.testmod()

dynamic_programming/sum_of_subset.py

@@ -29,6 +29,7 @@ def isSumSubset(arr, arrLen, requiredSum):
     #     print(subset[i])
     print(subset[arrLen][requiredSum])
 
+
 if __name__ == "__main__":
     import doctest