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libvieter
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feat(tree): first attempt at wikipedia pseudo code

red-black-tree
Jef Roosens 2023-01-30 12:28:08 +01:00
parent 1d458c68a4
commit 17c2e15385
1 changed files with 92 additions and 0 deletions
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92
src/tree/vieter_tree_balancing.c
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@ -124,6 +124,22 @@ void vieter_tree_node_balance_after_insert(vieter_tree_node *node) {
} }
} }
vieter_tree_node *vieter_tree_node_rotate(vieter_tree_node *old_root,
bool dir) {
vieter_tree_node *new_root = old_root->children[1 - dir];
// Right rotation
if (dir) {
vieter_tree_node_set_child(old_root, new_root->children[1], false);
vieter_tree_node_set_child(new_root, old_root, true);
} else {
vieter_tree_node_set_child(old_root, new_root->children[0], true);
vieter_tree_node_set_child(new_root, old_root, false);
}
return new_root;
}
void vieter_tree_node_remove_balanced(vieter_tree_node *node) { void vieter_tree_node_remove_balanced(vieter_tree_node *node) {
// A red node can only have 0 or 2 children. The node we receive only has // A red node can only have 0 or 2 children. The node we receive only has
// one child at most, so we know if it's red that it doesn't have any // one child at most, so we know if it's red that it doesn't have any
@ -145,4 +161,80 @@ void vieter_tree_node_remove_balanced(vieter_tree_node *node) {
} }
// The complicated case is when we want to remove a black leaf // The complicated case is when we want to remove a black leaf
// https://en.wikipedia.org/wiki/Red%E2%80%93black_tree#Removal_of_a_black_non-root_leaf
vieter_tree_node *parent = node->parent;
vieter_tree_node *sibling, *close_nephew, *distant_nephew;
bool dir = vieter_tree_node_get(node, vieter_tree_node_right);
parent->children[dir] = NULL;
vieter_tree_node_free(node);
goto start;
do {
dir = vieter_tree_node_get(node, vieter_tree_node_right);
start:
sibling = parent->children[1 - dir];
distant_nephew = sibling->children[1 - dir];
close_nephew = sibling->children[dir];
if (!vieter_tree_node_get(sibling, vieter_tree_node_black))
goto case3;
if (distant_nephew != NULL &&
!vieter_tree_node_get(distant_nephew, vieter_tree_node_black))
goto case6;
if (close_nephew != NULL &&
!vieter_tree_node_get(close_nephew, vieter_tree_node_black))
goto case5;
if (!vieter_tree_node_get(parent, vieter_tree_node_black))
goto case4;
// Case 2
vieter_tree_node_set(sibling, vieter_tree_node_black, false);
node = parent;
} while ((parent = node->parent) != NULL);
// Case 1
return;
case3:
vieter_tree_node_rotate(parent, dir);
vieter_tree_node_set(parent, vieter_tree_node_black, false);
vieter_tree_node_set(sibling, vieter_tree_node_black, true);
sibling = close_nephew;
distant_nephew = sibling->children[1 - dir];
if (distant_nephew != NULL &&
!vieter_tree_node_get(distant_nephew, vieter_tree_node_black))
goto case6;
close_nephew = sibling->children[dir];
if (close_nephew != NULL &&
!vieter_tree_node_get(close_nephew, vieter_tree_node_black))
goto case5;
case4:
vieter_tree_node_set(sibling, vieter_tree_node_black, false);
vieter_tree_node_set(parent, vieter_tree_node_black, true);
return;
case5:
vieter_tree_node_rotate(sibling, 1 - dir);
vieter_tree_node_set(sibling, vieter_tree_node_black, false);
vieter_tree_node_set(close_nephew, vieter_tree_node_black, true);
distant_nephew = sibling;
sibling = close_nephew;
case6:
vieter_tree_node_rotate(parent, dir);
vieter_tree_node_set(sibling, vieter_tree_node_black,
vieter_tree_node_get(parent, vieter_tree_node_black));
vieter_tree_node_set(parent, vieter_tree_node_black, true);
vieter_tree_node_set(distant_nephew, vieter_tree_node_black, true);
} }