Inserting element into left leaning black red tree c++ - c++

Question

I have been staring at this all day and have gotten slightly somewhere, but it's still not working correctly! Just trying to 'put' (really insert, or find if it's there) an element k into a LL red black tree. Here's my method:
Node * RPut(Node* p, const K& k, Node*& location)
{
// if you are at the bottom of the tree,
// add new node at bottom of the tree
if (p == 0)
{
// new red note with new data
location = NewNode(k, Data(), RED);
return location;
}
if(greater_(k,p->key_))
{
// if it's greater than the root, move down to the left child
p->left_ = Rput(p->left_, k, location);
}
// right subtree
else if (greater_(p->key_,k))
{
// but if the key is less than root, move down to right child
p->right_ = Rput(p->right_, k, location);
}
// if they are equal
else
{
location = p;
}
// code for rotating
// this sort of worked.
if(p->right_ && p->right_->IsRed())
{
p = RotateLeft(p);
if (p->left_->IsBlack())
{
p->SetBlack();
p->left_->SetRed();
}
}
if (p->left_ && p->left_->IsRed())
{ if (p->left_->left_ && p->left_->left_->IsRed())
{
p = RotateRight(p);
p->left_->SetBlack();
p->right_->SetBlack();
}
}
return p;
}
I know my rotate methods work perfectly. This inserts correctly until the fifth element (I haven't tried every combination, but usually.) For instance, abcde inserted correctly would be
d
b e
a c --
[with b as red node]
mine works but stops here, giving me:
b
a d
- - c e
with NO red nodes.
Anyone see anything obvious I am overlooking or why it isn't working properly? Any help at all much appreciated.
Thanks!

Answer 1

This does not directly answer the question, but have you read Sedgewick's paper on left-leaning red black trees? The code in it is exceptionally clear, there are beautiful diagrams explaining how things work, and, I imagine, it would be straight-forward to reimplement everything into C++.
Edit
I tried, for fun to implement Sedgewick's code. It turns out the paper had a few methods/subroutines left out that would have been pretty helpful to include. Anyway, my C++11 implementation, along with some tests, follows.
Since Java does automagic memory management, Sedgewick doesn't explicitly note where memory should be freed in his code. Rather than try to figure this out for a quick project and possibly leave memory leaks, I've opted to use std::shared_ptr, which provides a similar worry-free behaviour.
#include <iostream>
#include <vector>
#include <cstdlib>
#include <memory>
template<class keyt, class valuet>
class LLRB {
private:
static const bool COLOR_RED = true;
static const bool COLOR_BLACK = false;
class Node {
public:
keyt key;
valuet val;
std::shared_ptr<Node> right;
std::shared_ptr<Node> left;
bool color;
Node(keyt key, valuet val){
this->key = key;
this->val = val;
this->color = COLOR_RED;
this->right = nullptr;
this->left = nullptr;
}
};
typedef std::shared_ptr<Node> nptr;
nptr root;
nptr rotateLeft(nptr h){
nptr x = h->right;
h->right = x->left;
x->left = h;
x->color = h->color;
h->color = COLOR_RED;
return x;
}
nptr rotateRight(nptr h){
nptr x = h->left;
h->left = x->right;
x->right = h;
x->color = h->color;
h->color = COLOR_RED;
return x;
}
nptr moveRedLeft(nptr h){
flipColors(h);
if(isRed(h->right->left)){
h->right = rotateRight(h->right);
h = rotateLeft(h);
flipColors(h);
}
return h;
}
nptr moveRedRight(nptr h){
flipColors(h);
if(isRed(h->left->left)){
h = rotateRight(h);
flipColors(h);
}
return h;
}
void flipColors(nptr h){
h->color = !h->color;
h->left->color = !h->left->color;
h->right->color = !h->right->color;
}
bool isRed(const nptr h) const {
if(h==nullptr) return false;
return h->color == COLOR_RED;
}
nptr fixUp(nptr h){
if(isRed(h->right) && !isRed(h->left)) h = rotateLeft (h);
if(isRed(h->left) && isRed(h->left->left)) h = rotateRight(h);
if(isRed(h->left) && isRed(h->right)) flipColors (h);
return h;
}
nptr insert(nptr h, keyt key, valuet val){
if(h==nullptr)
return std::make_shared<Node>(key,val);
if (key == h->key) h->val = val;
else if(key < h->key) h->left = insert(h->left, key,val);
else h->right = insert(h->right,key,val);
h = fixUp(h);
return h;
}
//This routine probably likes memory
nptr deleteMin(nptr h){
if(h->left==nullptr) return nullptr;
if(!isRed(h->left) && !isRed(h->left->left))
h = moveRedLeft(h);
h->left = deleteMin(h->left);
return fixUp(h);
}
nptr minNode(nptr h){
return (h->left == nullptr) ? h : minNode(h->left);
}
//This routine leaks memory like no other!! I've added a few cleanups
nptr remove(nptr h, keyt key){
if(key<h->key){
if(!isRed(h->left) && !isRed(h->left->left))
h = moveRedLeft(h);
h->left = remove(h->left, key);
} else {
if(isRed(h->left))
h = rotateRight(h);
if(key==h->key && h->right==nullptr)
return nullptr;
if(!isRed(h->right) && !isRed(h->right->left))
h = moveRedRight(h);
if(key==h->key){
std::shared_ptr<Node> mn = minNode(h->right);
h->val = mn->val;
h->key = mn->key;
h->right = deleteMin(h->right);
} else {
h->right = remove(h->right, key);
}
}
return fixUp(h);
}
void traverse(const nptr h) const {
if(h==nullptr)
return;
traverse(h->left);
std::cout<< h->key << "=" << h->val <<std::endl;
traverse(h->right);
}
public:
LLRB(){
root = nullptr;
}
void traverse() const {
traverse(root);
}
valuet search(keyt key){
nptr x = root;
while(x!=nullptr){
if (key == x->key) return x->val;
else if (key < x->key) x=x->left;
else x=x->right;
}
return keyt();
}
void insert(keyt key, valuet val){
root = insert(root,key,val);
root->color = COLOR_BLACK;
}
void remove(keyt key){
root = remove(root,key);
root->color = COLOR_BLACK;
}
};
int main(){
for(int test=0;test<500;test++){
LLRB<int,int> llrb;
std::vector<int> keys;
std::vector<int> vals;
for(int i=0;i<1000;i++){
//Ensure each key is unique
int newkey = rand();
while(llrb.search(newkey)!=int())
newkey = rand();
keys.push_back(newkey);
vals.push_back(rand()+1);
llrb.insert(keys.back(),vals.back());
}
//llrb.traverse();
for(int i=0;i<1000;i++){
if(llrb.search(keys[i])!=vals[i]){
return -1;
}
}
for(int i=0;i<500;i++)
llrb.remove(keys[i]);
for(int i=500;i<1000;i++){
if(llrb.search(keys[i])!=vals[i]){
return -1;
}
}
}
std::cout<<"Good"<<std::endl;
}