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Improved Rope::rebalance() to actually rebalance properly in non-AVL cases.

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The prior version worked fine for the typical single insertion/removal
cases.  But when larger imbalances happened due to bulk insertion or
removal it wouldn't work correctly.

The new improved version works on any tree whose children are themselves
balanced, even if they are extremely different heights when compared to
each other.  It works in O(log N) time.
This commit is contained in:
Nathan Vegdahl 2015-02-18 23:11:10 -08:00
parent 535f219c41
commit d95161b88f
1 changed files with 71 additions and 47 deletions
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118
src/buffer/rope.rs
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@ -4,12 +4,13 @@ use std::str::Graphemes;
use std::ops::Index;
use string_utils::{grapheme_count, insert_text_at_grapheme_index, remove_text_between_grapheme_indices, split_string_at_grapheme_index, grapheme_pos_to_byte_pos};
const MIN_NODE_SIZE: usize = 64;
const MAX_NODE_SIZE: usize = MIN_NODE_SIZE * 2;
pub const MIN_NODE_SIZE: usize = 64;
pub const MAX_NODE_SIZE: usize = MIN_NODE_SIZE * 2;
/// A rope data structure for storing text in a format that is efficient
/// for insertion and removal even for extremely large strings.
#[derive(Debug)]
pub struct Rope {
data: RopeData,
grapheme_count_: usize,
@ -17,6 +18,7 @@ pub struct Rope {
}
#[derive(Debug)]
enum RopeData {
Leaf(String),
Branch(Box<Rope>, Box<Rope>),
@ -448,59 +450,56 @@ impl Rope {
}
/// Balances the tree under this node
/// Balances the tree under this node. Assumes that both the left and
/// right sub-trees are themselves aleady balanced.
fn rebalance(&mut self) {
loop {
let mut rot: isize;
if let RopeData::Branch(ref mut left, ref mut right) = self.data {
let height_diff = (left.tree_height as isize) - (right.tree_height as isize);
let mut rot: isize = 0;
if let RopeData::Branch(ref mut left, ref mut right) = self.data {
let height_diff = (left.tree_height as isize) - (right.tree_height as isize);
// Left side higher than right side
if height_diff > 1 {
let mut child_rot = false;
if let RopeData::Branch(ref lc, ref rc) = left.data {
if lc.tree_height < rc.tree_height {
child_rot = true;
}
// Left side higher than right side
if height_diff > 1 {
let mut child_rot = false;
if let RopeData::Branch(ref lc, ref rc) = left.data {
if lc.tree_height < rc.tree_height {
child_rot = true;
}
if child_rot {
left.rotate_left();
}
rot = 1;
}
// Right side higher then left side
else if height_diff < -1 {
let mut child_rot = false;
if let RopeData::Branch(ref lc, ref rc) = right.data {
if lc.tree_height > rc.tree_height {
child_rot = true;
}
}
if child_rot {
right.rotate_right();
}
rot = -1;
if child_rot {
left.rotate_left();
}
// Balanced, stop
else {
break;
rot = 1;
}
// Right side higher then left side
else if height_diff < -1 {
let mut child_rot = false;
if let RopeData::Branch(ref lc, ref rc) = right.data {
if lc.tree_height > rc.tree_height {
child_rot = true;
}
}
if child_rot {
right.rotate_right();
}
rot = -1;
}
else {
// Leaf node, stop
break;
}
if rot == 1 {
self.rotate_right();
if let RopeData::Branch(_, ref mut right) = self.data {
right.rebalance();
}
if rot == 1 {
self.rotate_right();
}
else if rot == -1 {
self.rotate_left();
}
else if rot == -1 {
self.rotate_left();
if let RopeData::Branch(ref mut left, _) = self.data {
left.rebalance();
}
}
}
@ -629,6 +628,7 @@ impl<'a> Iterator for RopeGraphemeIter<'a> {
#[cfg(test)]
mod tests {
use std::iter;
use super::*;
@ -1273,6 +1273,30 @@ mod tests {
assert!(Some("9") == iter.next());
assert!(None == iter.next());
}
#[test]
fn rebalance_1() {
let mut rope1 = Rope::new_from_str(String::from_utf8(vec!['c' as u8; MAX_NODE_SIZE]).unwrap().as_slice());
rope1.insert_text_at_grapheme_index(String::from_utf8(vec!['c' as u8; MAX_NODE_SIZE * 1024]).unwrap().as_slice(), MAX_NODE_SIZE);
let mut rope2 = Rope::new_from_str(String::from_utf8(vec!['c' as u8; MAX_NODE_SIZE * 1025]).unwrap().as_slice());
assert_eq!(rope1.tree_height, rope2.tree_height);
}
#[test]
fn rebalance_2() {
let mut rope1 = Rope::new_from_str(String::from_utf8(vec!['c' as u8; MAX_NODE_SIZE * 1024]).unwrap().as_slice());
rope1.remove_text_between_grapheme_indices(MAX_NODE_SIZE*7, MAX_NODE_SIZE*(7+959));
let mut rope2 = Rope::new_from_str(String::from_utf8(vec!['c' as u8; MAX_NODE_SIZE * 65]).unwrap().as_slice());
assert_eq!(rope1.tree_height, rope2.tree_height);
}
}
#[cfg(test)]