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Fix for erase losing RB Tree Property #67

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Merged
5cript merged 4 commits into from
Aug 30, 2026
Merged

Fix for erase losing RB Tree Property #67

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d461825
Added tests to check for red black tree damage on erase.
5cript Aug 29, 2026
62b925a
Fixed red black damage after erase.
5cript Aug 29, 2026
eb49cf9
Fixed tests that were depending on invalid fixup behavior.
5cript Aug 29, 2026
999587f
Added tests for fixed erase cases.
5cript Aug 30, 2026
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27 changes: 15 additions & 12 deletions include/interval-tree/interval_tree.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1180,10 +1180,11 @@ namespace lib_interval_tree
x->parent_ = y->parent_;

auto* x_parent = y->parent_;
const bool y_was_left = y->parent_ && y->is_left();

if (!y->parent_)
root_ = x;
else if (y->is_left())
else if (y_was_left)
y->parent_->left_ = x;
else
y->parent_->right_ = x;
Expand All @@ -1195,12 +1196,12 @@ namespace lib_interval_tree
recalculate_max(iter.node_);
}

if (x && x->color_ == rb_color::red)
if (y->color_ == rb_color::black)
{
if (x_parent)
erase_fixup(x, x_parent, y->is_left());
else
if (x && x->color_ == rb_color::red)
x->color_ = rb_color::black;
else if (x_parent)
erase_fixup(x, x_parent, y_was_left);
}

delete y;
Expand Down Expand Up @@ -2094,7 +2095,7 @@ namespace lib_interval_tree
{
tree_hooks::template on_before_erase_fixup<this_type>(*this, x, x_parent, y_is_left);

while (x != root_ && x->color_ == rb_color::black)
while (x != root_ && (!x || x->color_ == rb_color::black))
{
node_type* w;
if (y_is_left)
Expand All @@ -2108,16 +2109,17 @@ namespace lib_interval_tree
w = x_parent->right_;
}

if (w->left_->color_ == rb_color::black && w->right_->color_ == rb_color::black)
if ((!w->left_ || w->left_->color_ == rb_color::black) &&
(!w->right_ || w->right_->color_ == rb_color::black))
{
w->color_ = rb_color::red;
x = x_parent;
x_parent = x->parent_;
y_is_left = (x == x_parent->left_);
y_is_left = x_parent && (x == x_parent->left_);
}
else
{
if (w->right_->color_ == rb_color::black)
if (!w->right_ || w->right_->color_ == rb_color::black)
{
w->left_->color_ = rb_color::black;
w->color_ = rb_color::red;
Expand Down Expand Up @@ -2146,16 +2148,17 @@ namespace lib_interval_tree
w = x_parent->left_;
}

if (w->right_->color_ == rb_color::black && w->left_->color_ == rb_color::black)
if ((!w->right_ || w->right_->color_ == rb_color::black) &&
(!w->left_ || w->left_->color_ == rb_color::black))
{
w->color_ = rb_color::red;
x = x_parent;
x_parent = x->parent_;
y_is_left = (x == x_parent->left_);
y_is_left = x_parent && (x == x_parent->left_);
}
else
{
if (w->left_->color_ == rb_color::black)
if (!w->left_ || w->left_->color_ == rb_color::black)
{
w->right_->color_ = rb_color::black;
w->color_ = rb_color::red;
Expand Down
1 change: 1 addition & 0 deletions tests/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,7 @@ target_compile_options(tree-tests PUBLIC "$<$<CONFIG:RELEASE>:${RELEASE_OPTIONS}

if (INT_TREE_DRAW_EXAMPLES)
target_link_libraries(tree-tests PRIVATE cairo-wrap cairo)
target_compile_definitions(tree-tests PRIVATE INT_TREE_DRAW_EXAMPLES)
endif()

# If msys2, copy dynamic libraries to executable directory, visual studio does this automatically.
Expand Down
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