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feat(rtl): use one sentinel nil node globally

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Loïc Grégoire
2026-04-05 22:55:12 -04:00
parent 5341e057d2
commit 6a8fcaeebc
4 changed files with 66 additions and 52 deletions
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src/rtl/rbtree.zig
+30 -35
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@@ -68,8 +68,10 @@ pub fn RBTree(comptime cmp: fn (*bst.Node, *bst.Node) std.math.Order) type {
node.parent.set_ptr(y);
}
pub fn init(self: *Self) void {
self.tree.init();
pub fn init() Self {
return Self{
.tree = bst.BST(cmp).init(),
};
}
/// Insert the node `elem` into the tree.
@@ -157,7 +159,7 @@ pub fn RBTree(comptime cmp: fn (*bst.Node, *bst.Node) std.math.Order) type {
/// Delete the node `elem` from the tree.
pub fn delete(self: *Self, elem: *bst.Node) void {
var node = elem;
var child = &self.tree.nil;
var child = &bst.nil;
var orig_color = get_color(node);
if (self.tree.is_nil(node.left)) {
@@ -304,10 +306,17 @@ fn check_invariants(tree: *RBTree(cmp_test_node)) !void {
_ = try get_black_height(tree, tree.tree.root);
}
test "invariants hold after each insertion" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
fn make_tree() RBTree(cmp_test_node) {
bst.init_nil();
return .init();
}
fn insert_all(tree: *RBTree(cmp_test_node), nodes: []TestNode) !void {
for (nodes) |*n| try tree.insert(&n.node);
}
test "invariants hold after each insertion" {
var tree = make_tree();
var nodes = [_]TestNode{
.{ .value = 10, .node = undefined },
.{ .value = 5, .node = undefined },
@@ -319,7 +328,6 @@ test "invariants hold after each insertion" {
.{ .value = 3, .node = undefined },
.{ .value = 6, .node = undefined },
};
for (&nodes) |*n| {
try tree.insert(&n.node);
try check_invariants(&tree);
@@ -327,33 +335,28 @@ test "invariants hold after each insertion" {
}
test "ascending insertion stays balanced" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var tree = make_tree();
var nodes: [10]TestNode = undefined;
for (&nodes, 0..) |*n, i| {
n.value = @intCast(i + 1);
n.node = undefined;
n.* = .{ .value = @intCast(i + 1), .node = undefined };
try tree.insert(&n.node);
try check_invariants(&tree);
}
}
test "descending insertion stays balanced" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var tree = make_tree();
var nodes: [10]TestNode = undefined;
for (&nodes, 0..) |*n, i| {
n.value = @intCast(10 - i);
n.node = undefined;
n.* = .{ .value = @intCast(10 - i), .node = undefined };
try tree.insert(&n.node);
try check_invariants(&tree);
}
}
test "single insert and delete" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var n = TestNode{ .value = 69, .node = undefined };
var tree = make_tree();
var n = TestNode{ .value = 42, .node = undefined };
try tree.insert(&n.node);
try check_invariants(&tree);
tree.delete(&n.node);
@@ -361,37 +364,32 @@ test "single insert and delete" {
}
test "delete root" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var tree = make_tree();
var nodes = [_]TestNode{
.{ .value = 5, .node = undefined },
.{ .value = 3, .node = undefined },
.{ .value = 7, .node = undefined },
};
for (&nodes) |*n| try tree.insert(&n.node);
try insert_all(&tree, &nodes);
tree.delete(&nodes[0].node);
try check_invariants(&tree);
try std.testing.expect(!tree.tree.is_empty());
}
test "delete leaf" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var tree = make_tree();
var nodes = [_]TestNode{
.{ .value = 5, .node = undefined },
.{ .value = 3, .node = undefined },
.{ .value = 7, .node = undefined },
};
for (&nodes) |*n| try tree.insert(&n.node);
try insert_all(&tree, &nodes);
tree.delete(&nodes[1].node);
try check_invariants(&tree);
}
test "delete node with two children" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var tree = make_tree();
var nodes = [_]TestNode{
.{ .value = 10, .node = undefined },
.{ .value = 5, .node = undefined },
@@ -399,15 +397,13 @@ test "delete node with two children" {
.{ .value = 3, .node = undefined },
.{ .value = 7, .node = undefined },
};
for (&nodes) |*n| try tree.insert(&n.node);
try insert_all(&tree, &nodes);
tree.delete(&nodes[1].node);
try check_invariants(&tree);
}
test "invariants hold after each deletion" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var tree = make_tree();
var nodes = [_]TestNode{
.{ .value = 5, .node = undefined },
.{ .value = 3, .node = undefined },
@@ -419,7 +415,7 @@ test "invariants hold after each deletion" {
.{ .value = 1, .node = undefined },
.{ .value = 9, .node = undefined },
};
for (&nodes) |*n| try tree.insert(&n.node);
try insert_all(&tree, &nodes);
const delete_order = [_]usize{ 3, 0, 7, 1, 5, 2, 6, 4, 8 };
for (delete_order) |i| {
@@ -430,8 +426,7 @@ test "invariants hold after each deletion" {
}
test "duplicate insert returns error" {
var tree: RBTree(cmp_test_node) = undefined;
tree.init();
var tree = make_tree();
var a = TestNode{ .value = 5, .node = undefined };
var b = TestNode{ .value = 5, .node = undefined };
try tree.insert(&a.node);