github.com/songzhibin97/go-baseutils@v0.0.2-0.20240302024150-487d8ce9c082/structure/trees/redblacktree/iterator.go

package redblacktree

import "github.com/songzhibin97/go-baseutils/structure/containers"

// Assert Iterator implementation
var _ containers.ReverseIteratorWithKey[any, any] = (*Iterator[any, any])(nil)

// Iterator holding the iterator's state
type Iterator[K, V any] struct {
	tree     *Tree[K, V]
	node     *Node[K, V]
	position position
}

type position byte

const (
	begin, between, end position = 0, 1, 2
)

// Iterator returns a stateful iterator whose elements are key/value pairs.
func (tree *Tree[K, V]) Iterator() Iterator[K, V] {
	return Iterator[K, V]{tree: tree, node: nil, position: begin}
}

// IteratorAt returns a stateful iterator whose elements are key/value pairs that is initialised at a particular node.
func (tree *Tree[K, V]) IteratorAt(node *Node[K, V]) Iterator[K, V] {
	return Iterator[K, V]{tree: tree, node: node, position: between}
}

// Next moves the iterator to the next element and returns true if there was a next element in the container.
// If Next() returns true, then next element's key and value can be retrieved by Key() and Value().
// If Next() was called for the first time, then it will point the iterator to the first element if it exists.
// Modifies the state of the iterator.
func (iterator *Iterator[K, V]) Next() bool {
	if iterator.position == end {
		goto end
	}
	if iterator.position == begin {
		left := iterator.tree.Left()
		if left == nil {
			goto end
		}
		iterator.node = left
		goto between
	}
	if iterator.node.Right != nil {
		iterator.node = iterator.node.Right
		for iterator.node.Left != nil {
			iterator.node = iterator.node.Left
		}
		goto between
	}
	for iterator.node.Parent != nil {
		node := iterator.node
		iterator.node = iterator.node.Parent
		if node == iterator.node.Left {
			goto between
		}
	}

end:
	iterator.node = nil
	iterator.position = end
	return false

between:
	iterator.position = between
	return true
}

// Prev moves the iterator to the previous element and returns true if there was a previous element in the container.
// If Prev() returns true, then previous element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator[K, V]) Prev() bool {
	if iterator.position == begin {
		goto begin
	}
	if iterator.position == end {
		right := iterator.tree.Right()
		if right == nil {
			goto begin
		}
		iterator.node = right
		goto between
	}
	if iterator.node.Left != nil {
		iterator.node = iterator.node.Left
		for iterator.node.Right != nil {
			iterator.node = iterator.node.Right
		}
		goto between
	}
	for iterator.node.Parent != nil {
		node := iterator.node
		iterator.node = iterator.node.Parent
		if node == iterator.node.Right {
			goto between
		}
	}

begin:
	iterator.node = nil
	iterator.position = begin
	return false

between:
	iterator.position = between
	return true
}

// Value returns the current element's value.
// Does not modify the state of the iterator.
func (iterator *Iterator[K, V]) Value() V {
	return iterator.node.Value
}

// Key returns the current element's key.
// Does not modify the state of the iterator.
func (iterator *Iterator[K, V]) Key() K {
	return iterator.node.Key
}

// Node returns the current element's node.
// Does not modify the state of the iterator.
func (iterator *Iterator[K, V]) Node() *Node[K, V] {
	return iterator.node
}

// Begin resets the iterator to its initial state (one-before-first)
// Call Next() to fetch the first element if any.
func (iterator *Iterator[K, V]) Begin() {
	iterator.node = nil
	iterator.position = begin
}

// End moves the iterator past the last element (one-past-the-end).
// Call Prev() to fetch the last element if any.
func (iterator *Iterator[K, V]) End() {
	iterator.node = nil
	iterator.position = end
}

// First moves the iterator to the first element and returns true if there was a first element in the container.
// If First() returns true, then first element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator
func (iterator *Iterator[K, V]) First() bool {
	iterator.Begin()
	return iterator.Next()
}

// Last moves the iterator to the last element and returns true if there was a last element in the container.
// If Last() returns true, then last element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator[K, V]) Last() bool {
	iterator.End()
	return iterator.Prev()
}

// NextTo moves the iterator to the next element from current position that satisfies the condition given by the
// passed function, and returns true if there was a next element in the container.
// If NextTo() returns true, then next element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator[K, V]) NextTo(f func(key K, value V) bool) bool {
	for iterator.Next() {
		key, value := iterator.Key(), iterator.Value()
		if f(key, value) {
			return true
		}
	}
	return false
}

// PrevTo moves the iterator to the previous element from current position that satisfies the condition given by the
// passed function, and returns true if there was a next element in the container.
// If PrevTo() returns true, then next element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator[K, V]) PrevTo(f func(key K, value V) bool) bool {
	for iterator.Prev() {
		key, value := iterator.Key(), iterator.Value()
		if f(key, value) {
			return true
		}
	}
	return false
}