use core::alloc::Allocator;
use core::borrow::Borrow;
use super::node::ForceResult::*;
use super::node::Root;
use super::search::SearchResult::*;
impl<K, V> Root<K, V> {
/// Calculates the length of both trees that result from splitting up
/// a given number of distinct key-value pairs.
pub fn calc_split_length(
total_num: usize,
root_a: &Root<K, V>,
root_b: &Root<K, V>,
) -> (usize, usize) {
let (length_a, length_b);
if root_a.height() < root_b.height() {
length_a = root_a.reborrow().calc_length();
length_b = total_num - length_a;
debug_assert_eq!(length_b, root_b.reborrow().calc_length());
} else {
length_b = root_b.reborrow().calc_length();
length_a = total_num - length_b;
debug_assert_eq!(length_a, root_a.reborrow().calc_length());
}
(length_a, length_b)
}
/// Split off a tree with key-value pairs at and after the given key.
/// The result is meaningful only if the tree is ordered by key,
/// and if the ordering of `Q` corresponds to that of `K`.
/// If `self` respects all `BTreeMap` tree invariants, then both
/// `self` and the returned tree will respect those invariants.
pub fn split_off<Q: ?Sized + Ord, A: Allocator + Clone>(&mut self, key: &Q, alloc: A) -> Self
where
K: Borrow<Q>,
{
let left_root = self;
let mut right_root = Root::new_pillar(left_root.height(), alloc.clone());
let mut left_node = left_root.borrow_mut();
let mut right_node = right_root.borrow_mut();
loop {
let mut split_edge = match left_node.search_node(key) {
// key is going to the right tree
Found(kv) => kv.left_edge(),
GoDown(edge) => edge,
};
split_edge.move_suffix(&mut right_node);
match (split_edge.force(), right_node.force()) {
(Internal(edge), Internal(node)) => {
left_node = edge.descend();
right_node = node.first_edge().descend();
}
(Leaf(_), Leaf(_)) => break,
_ => unreachable!(),
}
}
left_root.fix_right_border(alloc.clone());
right_root.fix_left_border(alloc);
right_root
}
/// Creates a tree consisting of empty nodes.
fn new_pillar<A: Allocator + Clone>(height: usize, alloc: A) -> Self {
let mut root = Root::new(alloc.clone());
for _ in 0..height {
root.push_internal_level(alloc.clone());
}
root
}
}