Added more details about the problem statement (#1367)

* Update DIRECTORY

* Updated DIRECTORY

* Fixed bug in directory build and re-build the directory.md

* fixed url issue

* fixed indentation in Directory.md

* Add problem-18 of project-euler

* Delete sol1.py

* Delete files

* Added more details to question

* Added doctest in printNGE()

* Made changes to fix Travis CI build

* Remove the trailing whitespace

data_structures/stacks/next_greater_element.py

@@ -1,6 +1,13 @@
-# Function to print element and NGE pair for all elements of list
 def printNGE(arr):
-
+    """
+    Function to print element and Next Greatest Element (NGE) pair for all elements of list
+    NGE - Maximum element present afterwards the current one which is also greater than current one
+    >>> printNGE([11,13,21,3])
+    11 -- 13
+    13 -- 21
+    21 -- -1
+    3 -- -1
+    """
     for i in range(0, len(arr), 1):
 
         next = -1