Struct SumTree 

pub struct SumTree { /* private fields */ }

Sum-tree over capacity leaves backed by a flat Vec<f32>.

Used by super::PrioritizedReplayBuffer to draw transitions with probability proportional to their priority. The tree itself doesn’t know about transitions — the buffer maintains the leaf-to-transition mapping separately.

Implementations

impl SumTree

pub fn new(capacity: usize) -> Self

Create a new sum-tree with all priorities initialized to zero.

Arguments

• capacity - Number of leaves. Must be > 0.

Panics

Panics if capacity == 0.

pub fn total(&self) -> f32

Total priority (the root of the tree).

pub fn capacity(&self) -> usize

Number of leaves.

pub fn max_leaf(&self) -> f32

Maximum priority across all leaves.

Used by super::PrioritizedReplayBuffer::push to assign a freshly inserted transition a priority that guarantees it gets sampled at least once.

pub fn leaf_priority(&self, leaf_idx: usize) -> f32

Read the priority of leaf leaf_idx ∈ [0, capacity).

Panics

Panics if leaf_idx >= capacity.

pub fn update(&mut self, leaf_idx: usize, priority: f32)

Set the priority of leaf leaf_idx ∈ [0, capacity) to priority, propagating the delta up to the root.

Panics

Panics if leaf_idx >= capacity or priority is not finite or is negative.

pub fn find(&self, p: f32) -> (usize, f32)

Find the leaf whose cumulative-priority interval contains p.

Returns (leaf_idx, priority). The walk is deterministic: at each internal node we descend left if p ≤ left_child, else we subtract the left child’s value from p and descend right.

The caller is responsible for ensuring p ∈ [0, total()]; values slightly above total() are clamped by the walk so that the rightmost non-zero leaf is returned.

Panics

Panics if total() == 0 (cannot sample from a zero-priority tree).

Trait Implementations

impl Clone for SumTree

fn clone(&self) -> SumTree

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SumTree

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.