avltriee 0.77.2

Customized version of AVLTree library.Process the same value in the third branch. One data is immovable from one row, and positional relationships such as left, right, and parent are all referenced by row numbers. No search is required for value reference by specifying a row.
Documentation 
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use std::num::NonZeroU32;

use crate::{Avltriee, AvltrieeAllocator};

impl<T, I: ?Sized, A: AvltrieeAllocator<T>> Avltriee<T, I, A> {
    fn delete_same(&mut self, delete_row: NonZeroU32) {
        let delete_node = unsafe { self.node_unchecked(delete_row) };

        let delete_node_same = delete_node.same.unwrap();
        let delete_node_parent = delete_node.parent;
        let delete_node_height = delete_node.height;
        let delete_node_left = delete_node.left;
        let delete_node_right = delete_node.right;

        let new_node = unsafe { self.node_unchecked_mut(delete_node_same) };

        new_node.parent = delete_node_parent;
        new_node.height = delete_node_height;
        new_node.left = delete_node_left;
        new_node.right = delete_node_right;

        if let Some(left) = delete_node_left {
            unsafe { self.node_unchecked_mut(left) }.parent = Some(delete_node_same);
        }
        if let Some(right) = delete_node_right {
            unsafe { self.node_unchecked_mut(right) }.parent = Some(delete_node_same);
        }
    }

    fn delete_intermediate(&mut self, delete_row: NonZeroU32) -> (NonZeroU32, NonZeroU32) {
        let delete_node = unsafe { self.node_unchecked(delete_row) };

        let delete_node_left = delete_node.left;
        let delete_node_right = delete_node.right;
        let delete_node_parent = delete_node.parent;
        let delete_node_height = delete_node.height;

        let left_max = self.max(delete_node_left).unwrap();

        unsafe { self.node_unchecked_mut(left_max) }.right = delete_node_right;
        unsafe { self.node_unchecked_mut(delete_node_right.unwrap()) }.parent = Some(left_max);

        if delete_node_left == Some(left_max) {
            unsafe { self.node_unchecked_mut(left_max) }.parent = delete_node_parent;
            self.reset_height(left_max);
            (left_max, left_max)
        } else {
            let left_max_node = unsafe { self.node_unchecked_mut(left_max) };

            let left_max_parent = left_max_node.parent.unwrap();
            let left_max_left = left_max_node.left;

            left_max_node.height = delete_node_height;
            left_max_node.left = delete_node_left;
            unsafe { self.node_unchecked_mut(delete_node_left.unwrap()) }.parent = Some(left_max);

            unsafe { self.node_unchecked_mut(left_max_parent) }.right = left_max_left;
            if let Some(right) = left_max_left {
                unsafe { self.node_unchecked_mut(right) }.parent = Some(left_max_parent);
            }

            (left_max, left_max_parent)
        }
    }

    pub(crate) fn delete_inner(&mut self, row: NonZeroU32) {
        if let Some(node) = self.node(row) {
            let row_parent = node.parent;
            let same = node.same;
            if let Some(row_parent_inner) = row_parent {
                let parent_same = unsafe { self.node_unchecked_mut(row_parent_inner) }.same;
                if parent_same == Some(row) {
                    unsafe { self.node_unchecked_mut(row_parent_inner) }.same = same;
                    if same.is_some() {
                        self.delete_same(row);
                    }
                } else if let Some(same) = same {
                    unsafe { self.node_unchecked_mut(row_parent_inner) }
                        .changeling(row, Some(same));
                    self.delete_same(row);
                } else {
                    let left = unsafe { self.node_unchecked(row) }.left;
                    let right = unsafe { self.node_unchecked(row) }.right;
                    if left.is_none() {
                        unsafe { self.node_unchecked_mut(row_parent_inner) }.changeling(row, right);
                        if let Some(right) = right {
                            unsafe { self.node_unchecked_mut(right) }.parent = row_parent;
                        }
                        self.balance(row_parent_inner);
                    } else if right.is_none() {
                        unsafe { self.node_unchecked_mut(row_parent_inner) }.changeling(row, left);
                        unsafe { self.node_unchecked_mut(left.unwrap()) }.parent = row_parent;
                        self.balance(row_parent_inner);
                    } else {
                        let (new_row, balance_row) = self.delete_intermediate(row);
                        unsafe { self.node_unchecked_mut(row_parent_inner) }
                            .changeling(row, Some(new_row));
                        let delete_row_height = unsafe { self.node_unchecked(row) }.height;
                        let node = unsafe { self.node_unchecked_mut(new_row) };
                        node.height = delete_row_height;
                        node.parent = row_parent;
                        self.reset_height(balance_row);
                        self.balance(balance_row);
                    }
                }
            } else {
                if same.is_some() {
                    self.set_root(same);
                    self.delete_same(row);
                } else {
                    let left = node.left;
                    let right = node.right;
                    if left.is_none() {
                        if let Some(right) = right {
                            unsafe { self.node_unchecked_mut(right) }.parent = None;
                        }
                        self.set_root(right);
                    } else if right.is_none() {
                        unsafe { self.node_unchecked_mut(left.unwrap()) }.parent = None;
                        self.set_root(left);
                    } else {
                        let (new_row, balance_row) = self.delete_intermediate(row);
                        self.set_root(Some(new_row));
                        unsafe { self.node_unchecked_mut(new_row) }.parent = None;
                        self.reset_height(balance_row);
                        self.balance(balance_row);
                    }
                }
            }
            unsafe { self.node_unchecked_mut(row) }.height = 0;

            if row.get() == self.rows_count() {
                let mut current = row.get() - 1;
                if current > 0 {
                    while unsafe { self.allocator.get(NonZeroU32::new_unchecked(current)) }
                        .is_none()
                    {
                        current -= 1;
                        if current == 0 {
                            break;
                        }
                    }
                }
                self.set_rows_count(current);
            }
        }
    }
}