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use crate::{stack::Stack, Node};
#[repr(transparent)]
pub struct BuildTreeState<S: Stack>(S);
impl<S: Stack> BuildTreeState<S> {
pub fn new(i: &impl Iterator<Item = S::Node>) -> Self {
Self(S::with_capacity(i))
}
// 00 => 0 []
// 01 => 1 [0]
// 02 => 1 [1]
// 03 => 2 [1,0]
// 04 => 2 [1,1],[2]
// 05 => 2 [2,0]
// 06 => 2 [2,1]
// 07 => 3 [2,1,0]
// 08 => 3 [2,2],[3]
// 09 => 3 [3,0]
// 0A => 3 [3,1]
// 0B => 3 [3,1,0]
// 0C => 3 [3,1,1],[3,2]
// 0D => 3 [3,2,0]
// 0E => 3 [3,2,1]
// 0F => 4 [3,2,1,0]
// 10 => 4 [3,2,1,1],[3,2,2],[3,3],[4]
// 11 => 4 [4,0]
// ...
// 1E => 4 [4,3,2,1]
// 1F => 5 [4,3,2,1,0]
// 20 => 5 [4,3,2,1,1],[4,3,2,2],[4,3,3],[4,4],[5]
// ...
// 3E => 5 [5,4,3,2,1]
// 3F => 6 [5,4,3,2,1,0]
// 40 => 6 [5,4,3,2,1,1],[5,4,3,2,2],[5,4,3,3],[5,4,4],[5,5],[6]
pub fn fold_op(mut self, mut right: S::Node) -> Self {
let mut right_level = 0;
loop {
match self.0.pop_if(right_level) {
Some(left) => {
right = left.new_parent(right);
right_level += 1;
}
_ => break,
}
}
self.0.push((right, right_level));
self
}
pub fn collect(self) -> Option<S::Node> {
self.0
.reduce(|(mut right, mut right_level), (left, left_level)| {
while left_level > right_level {
right = right.new_parent_from_single();
right_level += 1;
}
(left.new_parent(right), right_level + 1)
})
.map(|(v, _)| v)
}
}
#[cfg(test)]
mod tests {
use crate::VecStack;
use super::*;
#[derive(Clone, Default, PartialEq, Eq, Debug)]
struct Sum(usize);
impl Node for Sum {
fn new_parent(self, right: Self) -> Self {
Sum(self.0 + right.0)
}
fn new_parent_from_single(self) -> Self {
self
}
}
pub struct DebugStack<T: Node> {
vec: VecStack<T>,
max_len: usize,
}
impl<T: Node> Stack for DebugStack<T> {
type Node = T;
fn with_capacity(i: &impl Iterator) -> Self {
Self {
vec: VecStack::with_capacity(i),
max_len: 0,
}
}
fn push(&mut self, value: (T, u8)) {
self.vec.push(value);
self.max_len = self.max_len.max(self.vec.stack.len());
}
fn pop_if(&mut self, level: u8) -> Option<T> {
self.vec.pop_if(level)
}
}
impl<T: Node> Iterator for DebugStack<T> {
type Item = (T, u8);
fn next(&mut self) -> Option<Self::Item> {
self.vec.next()
}
}
#[test]
fn sum() {
let f = |n| -> Option<usize> {
let i = (0..n).map(|v| Sum(v));
let state = BuildTreeState::<DebugStack<_>>::new(&i);
let capacity = state.0.vec.stack.capacity();
let new_state = i.fold(state, BuildTreeState::fold_op);
// `max_len` should be equivalent to `capacity`.
assert_eq!(new_state.0.max_len, capacity);
// a `set` should be equivalent to `n`.
assert_eq!(new_state.0.vec.set, n);
// the size of the final stack state should be a number of `1` bits in `n`.
assert_eq!(
new_state.0.vec.stack.len(),
n.count_ones() as usize,
"n: {n}"
);
new_state.collect().map(|v| v.0)
};
assert_eq!(f(0), None);
let g = |n| assert_eq!(f(n), Some(n * (n - 1) / 2));
for i in 1..10_000 {
g(i);
}
g(100_000_000);
}
}