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Balancing Tree to Prevent Skewness #1025

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Balancing Tree to Prevent Skewness #1025

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ca47fc7
optimize splay tree
m4ushold Oct 2, 2024
9952737
Trigger CI
raararaara Feb 21, 2025
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19 changes: 17 additions & 2 deletions pkg/splay/splay.go
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Original file line number Diff line number Diff line change
Expand Up @@ -92,13 +92,16 @@ func (t *Node[V]) hasLinks() bool {
// Tree is weighted binary search tree which is based on Splay tree.
// original paper on Splay Trees: https://www.cs.cmu.edu/~sleator/papers/self-adjusting.pdf
type Tree[V Value] struct {
root *Node[V]
root *Node[V]
linearCount int
firstNode *Node[V]
}

// NewTree creates a new instance of Tree.
func NewTree[V Value](root *Node[V]) *Tree[V] {
return &Tree[V]{
root: root,
root: root,
linearCount: 0,
}
}

Expand All @@ -114,6 +117,18 @@ func (t *Tree[V]) Insert(node *Node[V]) *Node[V] {

// InsertAfter inserts the node after the given previous node.
func (t *Tree[V]) InsertAfter(prev *Node[V], node *Node[V]) *Node[V] {
if prev == t.root {
t.linearCount++
if t.linearCount == 1 {
t.firstNode = node
} else if t.linearCount > 500 {
t.Splay(t.firstNode)
t.linearCount = 0
}
Comment on lines +122 to +127
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⚠️ Potential issue

Ensure firstNode is valid before splaying

There's a potential risk that firstNode might have been modified or removed from the tree before the splay operation when linearCount exceeds the threshold. This could lead to unexpected behavior or runtime errors. Consider adding a check to ensure that firstNode is still a valid node in the tree before performing the splay operation.

Apply this diff to include a validity check:

        } else if t.linearCount > 500 {
+           if t.isValidNode(t.firstNode) {
                t.Splay(t.firstNode)
+           }
            t.linearCount = 0
        }

And implement the isValidNode method:

func (t *Tree[V]) isValidNode(node *Node[V]) bool {
    return node != nil && node.hasLinks()
}

} else {
t.linearCount = 0
}

t.Splay(prev)
t.root = node
node.right = prev.right
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