From 236500bc03d18b10f0989e052f4e829b52ad03f0 Mon Sep 17 00:00:00 2001
From: Aleksander Sadikov <aleksander.sadikov@fri.uni-lj.si>
Date: Fri, 23 Sep 2016 18:49:19 +0200
Subject: English translation for quicksort/2 added.

---
 prolog/problems/sorting/quick_sort_2/en.py | 59 +++++++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)

(limited to 'prolog')

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>
+''',
+}
-- 
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