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ds: One step closer to fixing erasure for AVL tree
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I thought I had got it now, but changed a test and there are still
edgecases.
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@rHermes
rHermes committed Jul 12, 2024
1 parent 3bbc985 commit 4b6ca99
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Showing 2 changed files with 103 additions and 66 deletions.
165 changes: 100 additions & 65 deletions include/hage/ds/avl_tree.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
#include <sstream>
#include <stdexcept>
#include <unordered_map>
#include <utility>
#include <vector>

namespace hage::ds {
Expand Down Expand Up @@ -75,7 +76,6 @@ class AVLTree
constexpr iterator erase(iterator pos)
{
auto id = internal_erase(pos.m_id);
// std::ranges::copy_backward
return make_iterator(id);
}

Expand Down Expand Up @@ -640,22 +640,6 @@ class AVLTree

[[nodiscard]] constexpr node_id_type internal_erase(const node_id_type root)
{
auto shiftNodes = [&](const node_id_type orig, const node_id_type replace) {
auto parent = m_nodes[orig].m_parent;
if (parent == -1) {
m_root = replace;
} else if (orig == m_nodes[parent].m_left) {
m_nodes[parent].m_left = replace;
} else {
m_nodes[parent].m_right = replace;
}

if (replace != -1) {
m_nodes[replace].m_parent = parent;
}

return replace;
};

const auto retValue = next_node(root);

Expand All @@ -669,45 +653,83 @@ class AVLTree

// ok, we are going to

node_id_type newRoot = -1;
node_id_type newRoot = root;

// Ok, but it's here that the sausage will get made.
int firstNudge = 0;
bool lateCleanup = false;
auto& node = m_nodes[root];
if (node.m_left == -1) {
newRoot = shiftNodes(root, node.m_right);
if (node.m_left == -1 && node.m_right == -1) {
lateCleanup = true;
} else if (node.m_left == -1) {
newRoot = node.m_right;
auto root_right = node.m_right;
if (node.m_parent == -1) {
m_root = root_right;
} else {
if (m_nodes[node.m_parent].m_left == root) {
m_nodes[node.m_parent].m_left = root_right;
firstNudge = -1;
} else {
m_nodes[node.m_parent].m_right = root_right;
firstNudge = 1;
}
}

m_nodes[newRoot].m_parent = std::exchange(node.m_parent, newRoot);
} else if (node.m_right == -1) {
newRoot = shiftNodes(root, node.m_left);
newRoot = node.m_left;

auto root_left = node.m_left;
if (node.m_parent == -1) {
m_root = root_left;
} else {
if (m_nodes[node.m_parent].m_left == root) {
m_nodes[node.m_parent].m_left = root_left;
firstNudge = -1;
} else {
m_nodes[node.m_parent].m_right = root_left;
firstNudge = 1;
}
}

m_nodes[newRoot].m_parent = std::exchange(node.m_parent, newRoot);
} else {
// This is where we need change also internal balancing nodes.

auto next = retValue;
// ah, first we remove ourselves from this spot in the tree,
// and then we move ourselves into the tree.
if (m_nodes[next].m_parent != root) {
auto par = m_nodes[next].m_parent;
if (par != m_end) {
m_nodes[par].m_balance++;
}
auto& nextNode = m_nodes[next];

// ok, we have two children, we will do a bit of a meme here.
nextNode.m_left = std::exchange(node.m_left, -1);
m_nodes[nextNode.m_left].m_parent = next;

// This is correct, we need to run up a rebalance from this spot, until you reach the parent then?
nextNode.m_balance = std::exchange(node.m_balance, 0);

shiftNodes(next, m_nodes[next].m_right);
m_nodes[next].m_right = node.m_right;
m_nodes[node.m_right].m_parent = next;
if (node.m_parent == -1) {
m_root = next;
} else {
// hey
std::ignore = 1;
if (m_nodes[node.m_parent].m_left == root) {
m_nodes[node.m_parent].m_left = next;
} else {
m_nodes[node.m_parent].m_right = next;
}
}
newRoot = shiftNodes(root, next);
m_nodes[next].m_left = node.m_left;
m_nodes[node.m_left].m_parent = next;
}

// remove the root node.
free_node(root);
--m_size;
if (node.m_right != next) {
nextNode.m_right = std::exchange(node.m_right, -1);
m_nodes[nextNode.m_right].m_parent = next;

if (newRoot == -1) {
return retValue;
if (m_nodes[nextNode.m_parent].m_left == next) {
m_nodes[nextNode.m_parent].m_left = -1;
} else {
m_nodes[nextNode.m_parent].m_right = -1;
}
nextNode.m_parent = std::exchange(node.m_parent, nextNode.m_parent);

} else {
firstNudge = 1;
nextNode.m_parent = std::exchange(node.m_parent, next);
}
}

// OK, time to rebalance the tree, let's hope I can do it. With wikipedia as my guide it can work.
Expand All @@ -717,39 +739,42 @@ class AVLTree
int b = 0;

// BF(X) is not yet updated.
if (newRoot == m_nodes[parentNode].m_left) { // it's the left tree which decreases
if (0 < m_nodes[parentNode].m_balance) { // X is right heavy
// THe temporary BF(X) == +2 amd we need to rebalance
// we need to rebalance
auto Z = m_nodes[parentNode].m_right;
if (firstNudge == 1 || newRoot == m_nodes[parentNode].m_right) { // it's the right tree which decreases
firstNudge = 0;
// We are in the right subtree
if (m_nodes[parentNode].m_balance < 0) {
// parentNode is left heavy and we need to rebalance
auto Z = m_nodes[parentNode].m_left;
b = m_nodes[Z].m_balance;
if (b < 0) {
newRoot = rotate_right_left(parentNode, Z);

if (0 < b) {
newRoot = rotate_left_right(parentNode, Z);
} else {
newRoot = rotate_left(parentNode, Z);
newRoot = rotate_right(parentNode, Z);
}
} else {
auto pre = m_nodes[parentNode].m_balance++;
auto pre = m_nodes[parentNode].m_balance--;
if (pre == 0)
break;

newRoot = parentNode;
continue;
}
} else {
// We are in the right subtree
if (m_nodes[parentNode].m_balance < 0) {
// parentNode is left heavy and we need to rebalance
auto Z = m_nodes[parentNode].m_left;
b = m_nodes[Z].m_balance;
firstNudge = 0;

if (0 < b) {
newRoot = rotate_left_right(parentNode, Z);
if (0 < m_nodes[parentNode].m_balance) { // X is right heavy
// THe temporary BF(X) == +2 amd we need to rebalance
// we need to rebalance
auto Z = m_nodes[parentNode].m_right;
b = m_nodes[Z].m_balance;
if (b < 0) {
newRoot = rotate_right_left(parentNode, Z);
} else {
newRoot = rotate_right(parentNode, Z);
newRoot = rotate_left(parentNode, Z);
}
} else {
auto pre = m_nodes[parentNode].m_balance--;
auto pre = m_nodes[parentNode].m_balance++;
if (pre == 0)
break;

Expand All @@ -775,7 +800,16 @@ class AVLTree
break;
}

// Now let's think here.
if (lateCleanup && node.m_parent != -1) {
if (m_nodes[node.m_parent].m_left == root) {
m_nodes[node.m_parent].m_left = -1;
} else {
m_nodes[node.m_parent].m_right = -1;
}
}

free_node(root);
--m_size;
return retValue;
}

Expand Down Expand Up @@ -856,10 +890,11 @@ class AVLTree

void add_node_attrib(const std::string& sid, const std::string& key, const std::string& val, bool isHtml)
{
using namespace std::string_literals;
if (isHtml) {
m_nodes[sid][key] = "<" + val + ">";
m_nodes[sid][key] = "<"s + val + ">"s;
} else {
m_nodes[sid][key] = "\"" + val + "\"";
m_nodes[sid][key] = "\""s + val + "\""s;
}
}

Expand Down
4 changes: 3 additions & 1 deletion tests/avl_tree_tests.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -182,13 +182,15 @@ TEST_CASE("AVL erase tests")

SUBCASE("Erasing randomly should work")
{
std::ranlux48 rng{ 24 };
std::ranlux48 rng{ 123 };
std::ranges::shuffle(toDelete, rng);
for (auto toDel : toDelete) {
INFO("Doing: ", toDel);

/*
std::cout << "Going to delete: " << toDel << "\n";
std::cout << tree.print_dot_tree();
*/

auto it1 = tree.find(toDel);
REQUIRE_NE(it1, tree.end());
Expand Down

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