diff options
| -rw-r--r-- | prolog/problems/sorting/quick_sort_2/en.py | 59 |
1 files changed, 58 insertions, 1 deletions
diff --git a/prolog/problems/sorting/quick_sort_2/en.py b/prolog/problems/sorting/quick_sort_2/en.py index aa3eb44..a5b571b 100644 --- a/prolog/problems/sorting/quick_sort_2/en.py +++ b/prolog/problems/sorting/quick_sort_2/en.py @@ -8,4 +8,61 @@ description = '''\ L = [1,2,3,4,5]. </pre>''' -hint = {} +plan = ['''\ +<p>Divide and conquer! And use previous solutions, of course. :)</p> +''', '''\ +<p>Take the head away, use it as a pivot, divide the tail into smaller and larger elements. Use recursion on +so obtained sublists since both are shorter (in the worst case scenario shorter by just the head element -- +this also explains why quicksort works worst on already sorted lists). In the end simply combine the sublists.</p> +''', '''\ +<p>If list <code>L</code> is composed of head <code>P</code> and tail <code>T</code> and if the tail is +split into sublists containing smaller and larger elements, respectively, based on pivot <code>P</code>, and if +we assume the recursion sorts these two sublists into lists <code>SortedSmallerElems</code> and +<code>SortedGreaterElems</code>, and if finally we concatenate these two lists and add in between pivot/head +<code>P</code>, then this results in correctly sorted initial list <code>L</code>.</p> +'''] + +hint = { + 'eq_instead_of_equ': '''\ +<p>The operator <code>==</code> is "stricter" than operator <code>=</code> in the sense that +for the latter it is enough to be able to make the two operands equal (unification).</p> +<p>Of course, you can also solve the exercise without explicit use of either of these two operators, just +remember that unification is implicitly performed with the predicate's arguments (head of clause).</p> +''', + + 'eq_instead_of_equ_markup': '''\ +<p>Perhaps the operator for unification (=) would be better?</p> +''', + + 'base_case': '''\ +<p>Did you think of a base case? Which list can you sort without any effort whatsoever?</p> +''', + + 'recursive_case': '''\ +<p>The base case is ok. However, what about the general recursive case?</p> +''', + + 'predicate_always_false': '''\ +<p>It seems your predicate is <em>always</em> "false". Did you give it the correct name, +or is it perhaps misspelled?</p> +<p>If the name is correct, check whether something else is misspelled, perhaps there is a full stop instead of +a comma or vice versa, or maybe you typed a variable name in lowercase?</p> +<p>It is, of course, also possible that your conditions are too restrictive, or even impossible to satisfy +(as would be, for example, the condition that <code>X</code> is <em>simultaneously</em> smaller and greater than +<code>Y</code>, or something similarly impossible).</p> +''', + + 'timeout': '''\ +<p>Is there an infinite recursion at work here? How will it ever stop?</p> +<p>Or perhaps is there a missing, faulty, or simply incompatible (with the general recursive case) base case?</p> +''', + + 'arbitrary_base_case': '''\ +<p>How can the sorted list be anything whatsoever or a list with an arbitrary element? Did you use +a variable without an assigned value?</p> +''', + + 'forgotten_pivot': '''\ +<p>Did you, perhaps, forgot to put the pivot element back into the list when returning from recursion?</p> +''', +} |