Map fully commented barring hard_erase

Map.hpp

@@ -1,20 +1,25 @@
 #ifndef _POWELL_CS440
 #define _POWELL_CS440
 #include <algorithm>
-// uncomment on submission/performance test
-// #define NDEBUG
 #include <cassert>
 #include <memory>
 #include <stdexcept>
 #include <utility>
 namespace cs440 {
+
 // universal type defs here
+// unnamed namespace used to hide implementation details
+// from the end user
 namespace {
+
+// used to specify direction for specifying which child of a node
+// is being referred to as well as for specifying the direction of
+// rotation for the implementation of red-black tree rules
+enum class Direction { Left, Right };
 // technically having this stuff here instead of in a C++ file is wasteful but
 // 1) I'm lazy
 // 2) idk how to make the Color enum value an implementation detail which the
 // template can use but external code can't other than this
-enum class Direction { Left, Right };
 Direction operator!(Direction dir) {
   switch (dir) {
   case Direction::Left:
@@ -27,21 +32,27 @@ Direction operator!(Direction dir) {
 }
 enum class Color { Red, Black };
 } // namespace
+
 template <typename Key_T, typename Mapped_T> class Map {
   // Type definitions here
   using ValueType = std::pair<const Key_T, Mapped_T>;
   using internal_ValueType = std::pair<Key_T, Mapped_T>;
 
+  // Internal Tree node type, tree is implemented via pointers
   struct Node {
+    // magic number used to check if a node has been moved from
     int valid = 0x13371337;
+
+    // all raw pointers are non-owning
     Node *parent = nullptr;
+    Node *prev;
+    Node *next;
+    Map *map;
+
     std::unique_ptr<internal_ValueType> val;
     std::unique_ptr<Node> left;
     std::unique_ptr<Node> right;
     Color color;
-    Node *prev;
-    Node *next;
-    Map *map;
     Node(internal_ValueType val, Map *map)
         : parent{nullptr}, val{new internal_ValueType{val}}, left{}, right{},
           color{Color::Red}, prev{nullptr}, next{nullptr}, map{map} {}
@@ -130,6 +141,8 @@ template <typename Key_T, typename Mapped_T> class Map {
       this->map = rhs.map;
       return *this;
     }
+
+    // Node::child is useful when a non-owning reference to a child is needed
     Node *child(Direction dir) {
       switch (dir) {
       case Direction::Left:
@@ -150,6 +163,9 @@ template <typename Key_T, typename Mapped_T> class Map {
         assert(false);
       }
     }
+
+    // uchild is used when ownership of the child is needed in the same
+    // instance it is accessed
     std::unique_ptr<Node> uchild(Direction dir) {
       switch (dir) {
       case Direction::Left:
@@ -163,6 +179,10 @@ template <typename Key_T, typename Mapped_T> class Map {
     std::unique_ptr<Node> uchild(Node *child) {
       return this->uchild(this->which_child(child));
     }
+
+    // set_child is used due to varous methods returning a Direction
+    // and the code for setting the correct child given a direction
+    // being repetitive, trivial and important to get correct
     std::unique_ptr<Node> &set_child(Direction dir,
                                      std::unique_ptr<Node> new_child) {
 
@@ -193,12 +213,16 @@ template <typename Key_T, typename Mapped_T> class Map {
       }
       assert(false);
     }
+
     void erase_child(Node *n) { this->erase_child(this->which_child(n)); }
     void erase_child(Direction dir) {
+      // if the child being erased is the min or the max we need to update
+      // the min/max
       bool minmax = this->child(dir) == this->map->min ||
                     this->child(dir) == this->map->max;
-      // bringing ownership to this function scope so Deleter gets called at end
-      // of function and we can do reordering things
+
+      // bringing ownership to this function scope so destructor gets
+      // called at the end of function and we can do reordering things
       std::unique_ptr<Node> dropping;
       switch (dir) {
       case Direction::Right:
@@ -221,6 +245,9 @@ template <typename Key_T, typename Mapped_T> class Map {
         dropping->next->prev = dropping->prev;
       }
 
+      // Correctness: We can only remove the min and the max at the same time
+      // if there's only 1 node left in which case we can't have children
+      // and this method wouldn't be called
       if (minmax) {
         switch (dir) {
         case Direction::Left:
@@ -233,6 +260,9 @@ template <typename Key_T, typename Mapped_T> class Map {
         }
       }
     }
+
+    // Utility to reset previous and next pointers when we add/remove nodes
+    // from the tree
     void restore_ordering() {
       this->prev = this->calc_pred();
       this->next = this->calc_succ();
@@ -243,6 +273,10 @@ template <typename Key_T, typename Mapped_T> class Map {
         this->next->prev = this;
       }
     }
+
+    // predecessor will be one of the following
+    // 1) our Right-most child tracing down from our left child
+    // 2) The first ancestor which has us to their right
     Node *calc_pred() {
       if (this->left) {
         Node *ret = this->left.get();
@@ -260,6 +294,10 @@ template <typename Key_T, typename Mapped_T> class Map {
         return ret;
       }
     }
+
+    // succcessor will be one of the following
+    // 1) our Left-most child tracing down from our right child
+    // 2) The first ancestor which has us to their left
     Node *calc_succ() {
       if (this->right) {
         Node *ret = this->right.get();
@@ -277,14 +315,20 @@ template <typename Key_T, typename Mapped_T> class Map {
         return ret;
       }
     }
+
+    // Rotation is an operation that applies to three nodes of the red-black
+    // tree, namely the node it's applying to, that node's child and of
+    // opposite the given direction and that child's child in the direction
+    // replacing this node with it's child and that child with the grandchild
+    // alongside various other bits of shuffling needed to make that all work
     void rotate(Direction dir) {
 
       // cannot rotate nullptr
       assert(this != nullptr);
       // we can't be root for this rotate operation
       assert(this->parent != nullptr);
-      // if we're missing the child on the opposite direction this is an invalid
-      // rotation
+      // if we're missing the child on the opposite direction
+      // this is an invalid rotation
       assert(this->child(!dir));
 
       Direction m_dir = this->parent->which_child(this);
@@ -309,7 +353,7 @@ template <typename Key_T, typename Mapped_T> class Map {
     void restore_red_black_insert(Direction dir) {
       Node *self = this;
 
-      // infinite loop for case 2's sake, if tail recursion optimization was
+      // "infinite" loop for case 2's sake, if tail recursion optimization was
       // guaranteed I'd use tail recursion
       while (true) {
         Node *parent = self->parent;
@@ -320,7 +364,8 @@ template <typename Key_T, typename Mapped_T> class Map {
         }
 
         dir = parent->which_child(self);
-        // if this is violated it's a bug
+
+        // if this is violated it's a bug in which_child
         assert(parent->child(dir) == self);
 
         // parent is black so no violation no-op (case 1)
@@ -372,9 +417,13 @@ template <typename Key_T, typename Mapped_T> class Map {
     }
   };
 
-  // data needed for implementation
+  // Map: data needed for implementation
   std::unique_ptr<Node> root;
+  // Recalculating the size every time size is called is obviously bad for
+  // performance considering we can just increment/decrement this counter as
+  // needed
   std::size_t _size;
+  // as in the case of Node raw pointers are non-owning
   Node *min;
   Node *max;
 
@@ -384,6 +433,8 @@ public:
   class ReverseIterator;
   // public type definitions
   class Iterator {
+    // two pointers are used to handling incrementing/decrementing
+    // outside the bounds of the iterator
     Node *underlying;
     Node *store;
     Iterator(Node *ptr, Node *potential = nullptr)
@@ -394,6 +445,7 @@ public:
     friend ConstIterator;
     friend ReverseIterator;
     Iterator() = delete;
+    // we don't own any data so no reason not to have all default
     Iterator(const Iterator &rhs) = default;
     Iterator &operator=(const Iterator &) = default;
     ~Iterator() = default;
@@ -449,6 +501,7 @@ public:
       return !(lhs == rhs);
     }
   };
+  // Const Iterator simply exposes a const interface to Iterator
   class ConstIterator {
     Iterator underlying;
 
@@ -499,6 +552,9 @@ public:
       return !(lhs == rhs);
     }
   };
+
+  // ReverseIterator simply swaps increment and decrement operators on the
+  // normal iterator for it's implementation
   class ReverseIterator {
     Iterator underlying;
     ReverseIterator(const Iterator &underlying) : underlying{underlying} {}
@@ -539,7 +595,11 @@ public:
     }
   };
 
-  Map() : root{}, _size{0}, min{nullptr}, max{nullptr} {}
+  Map() : root{nullptr}, _size{0}, min{nullptr}, max{nullptr} {}
+
+  // Not initializing min and max in member initializer_list may not be
+  // strictly correct but they get initialized as the first thing in
+  // the constructor so practically speaking that should be fine
   Map(const Map &rhs)
       : root{std::make_unique<Node>(*rhs.root)}, _size{rhs._size} {
     this->min = this->root.get();
@@ -552,6 +612,10 @@ public:
     }
   }
   Map(Map &&rhs) : root{std::move(rhs.root)}, _size{rhs._size} {
+    // This code is being kept as is to avoid accidentally breaking something
+    // when all I'm intending to do is retroactively add comments
+    // However I think it can be removed in favor of simply copying
+    // min and max from rhs due to everything being done via pointers
     this->min = this->root.get();
     this->max = this->root.get();
     while (min->left) {
@@ -587,6 +651,9 @@ public:
     }
     return *this;
   }
+
+  // No reason to redo making an empty map or inserting values from an
+  // iterator when I already have that functionality via other methods
   Map(std::initializer_list<std::pair<const Key_T, Mapped_T>> items) : Map{} {
     this->insert(items.begin(), items.end());
   }
@@ -595,6 +662,14 @@ public:
 
 private:
   // private helpers
+
+  // This method was originally written due to root originally being
+  // std::optional<Node> rather than std::unique_ptr<Node>, the code can
+  // probably be refactored such that only node rotations are used
+  // the reason it wasn't is because it wasn't necessary to complete the
+  // assignment and I'd already done a full rewrite once and now I'm here
+  // just to add comments with minimal changes that should only affect
+  // style/clarity
   void rotate_root(Direction dir) {
     assert(root);
 
@@ -639,6 +714,13 @@ private:
     }
   }
 
+  // this method is templated because previously in development this trace
+  // template var was used in conjunction with if constexpr to enable/disable
+  // debug logging which showed the trace of how locate traversed the tree
+  // the likely reasoning for removing the logging is due to the C++ compiler
+  // available on university lab machines (which I expected this to be tested
+  // on) was too old to allow if constexpr and the default template value
+  // meant removing that logging was trivial
   template <bool trace = false>
   std::pair<Node const *, Direction> locate(const Key_T &key) const {
     Node const *ret_parent;
@@ -669,11 +751,17 @@ private:
     }
     return std::make_pair(ret_parent, ret_dir);
   }
+
+  // the hard case of removing a black leaf node in a red black tree
+  // All other cases are handled in core_erase
   void hard_erase(Node *n) {
     assert(n->parent);
     Node *parent = n->parent;
     Direction dir = parent->which_child(n);
     parent->erase_child(n);
+
+    // case 1 should be handled first for all but the first loop
+    // so it's skipped in the first loop
     goto skip;
     while (true) {
       parent = n->parent;
@@ -694,7 +782,10 @@ private:
       Color close_color = close ? close->color : Color::Black;
       Color distant_color = distant ? distant->color : Color::Black;
 
+      // Macro is used for simplicity and avoiding repetition
 #define redcheck(v) if ((v) == Color::Red)
+
+      // TODO: continue comment writing here
       // it kinda sucks but I think that goto is genuinely the best solution
       // here, making methods for cases 4,5 and 6 is a lot of unneeded
       // bookkeeping
@@ -765,6 +856,17 @@ private:
       }
     }
   }
+
+  // https://en.wikipedia.org/wiki/Red%E2%80%93black_tree#Simple_cases
+  // core_erase is the low level erase level that handles
+  // all the easy cases for erasure, namely
+  // 1) nodes with two children (replacing the node with it's successor)
+  // 2) nodes with one child (replacing the node with it's child)
+  // 3) the root node (tree is empty)
+  // 4) red leaf nodes with no children (can simply be removed)
+  // Black leaf nodes are handled by calling out to hard_erase
+  // return value specifies whether or not successor and predecessor should
+  // be updated
   bool core_erase(Node *erasing) {
     Color c = erasing->color;
     // 2 children