bug fixed, AVL trees now working properly

Author: Alejandro Fernández Suárez

include/avl.h

@@ -51,8 +51,9 @@ class AVL {
 
  void erase(const T &x) {
  if (!isEmpty()) {
- tree = tree->erase(x);
- numNodes--;
+ bool found = false;
+ tree = tree->erase(x, found);
+ if (found) numNodes--;
  }
  }
 
@@ -64,7 +65,7 @@ class AVL {
  }
  }
 
- private:
+ public:
 
  struct Node {
  Node *left, *right;
@@ -93,51 +94,58 @@ class AVL {
  return update();
  }
 
- Node *erase(const T &x) {
+ Node *erase(const T &x, bool &found) {
  if (value == x) {
+ found = true;
  if (left == 0 && right == 0) {
  delete this;
  return 0;
  } else if (left == 0) {
+ Node *aux = right;
  *this = *right;
- delete right;
+ delete aux;
  } else if (right == 0) {
+ Node *aux = left;
  *this = *left;
- delete left;
+ delete aux;
  } else {
  // Tracing path to rightmost leaf of the left subtree
  std::stack<Node*> trace;
 
  Node *current = left;
- while (current->right != 0) {
+ while (current != 0) {
  trace.push(current);
  current = current->right;
  }
 
+ current = trace.top();
  value = current->value;
  Node *lsubtree = current->left;
  delete current;
+ trace.pop();
 
- if (trace.empty()) trace.push(left);
-
- trace.top()->right = lsubtree;
-
- do {
- trace.top()->update();
+ if (trace.empty()) { left = lsubtree; }
+ else {
+ trace.top()->right = lsubtree;
  trace.pop();
- } while (!trace.empty());
+ while (!trace.empty()) {
+ current = trace.top();
+ current->right = current->right->update();
+ trace.pop();
+ }
+ }
  }
  return update();
  }
  else if (x < value) {
  if (left != 0) {
- left = left->erase(x);
+ left = left->erase(x, found);
  return update();
  } else return this;
  }
  else {
  if (right != 0) {
- right = right->erase(x);
+ right = right->erase(x, found);
  return update();
  } else return this;
  }

src/avl_demo.cpp

@@ -5,7 +5,7 @@ using namespace std;
 using namespace alg;
 
 const unsigned N = 4096*32;
-const unsigned N_ELEMS_TO_REMOVE = 4096*8;
+const unsigned N_ELEMS_TO_REMOVE = N-128; // Must be between 0 and N-1
 
 template <typename T> 
 void printTreeStatus(const AVL<T> &t) {
@@ -40,20 +40,27 @@ int main()
  cout << "ERROR: Value " << values[idx] << " was inserted and not found!" << endl;
  }
 
- cout << "Now removing " << N_ELEMS_TO_REMOVE << " random elements for the tree... ";
+ cout << "Now removing a random element from the tree... ";
+ unsigned idx = rand() % N;
+ avl.erase(values[idx]);
+ cout << "Done" << endl;
+
+ printTreeStatus(avl);
+ 
+ cout << "Now removing the root of the tree " << N_ELEMS_TO_REMOVE << " times... ";
  for (unsigned i = 0; i < N_ELEMS_TO_REMOVE; ++i) {
- unsigned idx = rand() % N;
- avl.erase(values[idx]);
+ avl.erase(avl.root());
  }
  cout << "Done" << endl;
 
  printTreeStatus(avl);
 
- cout << "Do you want to see the GraphViz representation of the Tree (Y/n)? ";
+ // Outputting to cerr so the output can be redirected with ./avl_demo 2> <name>.gvz
+ cout << "Do you want to output the GraphViz representation of the tree to the cerr stream (Y/n)? ";
  char usrInput;
  cin >> usrInput;
- if (usrInput == 'Y' || usrInput == 'y') avl.toGraphViz(cout, "AVL");
-
+ if (usrInput == 'Y' || usrInput == 'y') avl.toGraphViz(cerr, "AVL");
+ 
  return 0;
 }