structure/vbtkey/iterator.go

package avlindex

import (
	"474420502.top/eson/structure/lastack"
)

type Iterator struct {
	dir    int
	up     *Node
	cur    *Node
	tstack *lastack.Stack
	// curnext *Node
}

func initIterator(avltree *Tree) *Iterator {
	iter := &Iterator{tstack: lastack.New()}
	iter.up = avltree.root
	return iter
}

func NewIterator(n *Node) *Iterator {
	iter := &Iterator{tstack: lastack.New()}
	iter.up = n
	return iter
}

func (iter *Iterator) Value() interface{} {
	return iter.cur.value
}

func (iter *Iterator) Left() bool {
	if iter.cur.children[0] != nil {
		iter.dir = 0
		iter.cur = iter.cur.children[0]
		return true
	}
	return false
}

func (iter *Iterator) Right() bool {
	if iter.cur.children[1] != nil {
		iter.dir = 0
		iter.cur = iter.cur.children[1]
		return true
	}
	return false
}

func GetPrev(cur *Node, idx int) *Node {

	iter := NewIterator(cur)
	iter.curPushPrevStack(iter.up)
	iter.up = iter.getPrevUp(iter.up)

	for i := 0; i < idx; i++ {

		if iter.tstack.Size() == 0 {
			if iter.up == nil {
				return nil
			}
			iter.tstack.Push(iter.up)
			iter.up = iter.getPrevUp(iter.up)
		}

		if v, ok := iter.tstack.Pop(); ok {
			iter.cur = v.(*Node)
			if i == idx-1 {
				return iter.cur
			}
			iter.curPushPrevStack(iter.cur)
		} else {
			return nil
		}
	}

	return cur
}

func (iter *Iterator) Prev() (result bool) {

	if iter.dir > -1 {
		if iter.dir == 1 && iter.cur != nil {
			iter.tstack.Clear()
			iter.curPushPrevStack(iter.cur)
			iter.up = iter.getPrevUp(iter.cur)
		}
		iter.dir = -1
	}

	if iter.tstack.Size() == 0 {
		if iter.up == nil {
			return false
		}
		iter.tstack.Push(iter.up)
		iter.up = iter.getPrevUp(iter.up)
	}

	if v, ok := iter.tstack.Pop(); ok {
		iter.cur = v.(*Node)
		iter.curPushPrevStack(iter.cur)
		return true
	}

	return false
}
func GetNext(cur *Node, idx int) *Node {

	iter := NewIterator(cur)
	iter.curPushNextStack(iter.up)
	iter.up = iter.getNextUp(iter.up)

	for i := 0; i < idx; i++ {

		if iter.tstack.Size() == 0 {
			if iter.up == nil {
				return nil
			}
			iter.tstack.Push(iter.up)
			iter.up = iter.getNextUp(iter.up)
		}

		if v, ok := iter.tstack.Pop(); ok {
			iter.cur = v.(*Node)
			if i == idx-1 {
				return iter.cur
			}
			iter.curPushNextStack(iter.cur)
		} else {
			return nil
		}
	}

	return cur
}

func (iter *Iterator) Next() (result bool) {

	if iter.dir < 1 { // 非 1(next 方向定义 -1 为 prev)
		if iter.dir == -1 && iter.cur != nil { // 如果上次为prev方向, 则清空辅助计算的栈
			iter.tstack.Clear()
			iter.curPushNextStack(iter.cur)    // 把当前cur计算的逆向回朔
			iter.up = iter.getNextUp(iter.cur) // cur 寻找下个要计算up
		}
		iter.dir = 1
	}

	// 如果栈空了, 把up的递归计算入栈, 重新计算 下次的up值
	if iter.tstack.Size() == 0 {
		if iter.up == nil {
			return false
		}
		iter.tstack.Push(iter.up)
		iter.up = iter.getNextUp(iter.up)
	}

	if v, ok := iter.tstack.Pop(); ok {
		iter.cur = v.(*Node)
		iter.curPushNextStack(iter.cur)
		return true
	}

	// 如果再次计算的栈为空, 则只能返回false
	return false
}

func getRelationship(cur *Node) int {
	if cur.parent.children[1] == cur {
		return 1
	}
	return 0
}

func (iter *Iterator) getNextUp(cur *Node) *Node {
	for cur.parent != nil {
		if getRelationship(cur) == 1 { // next 在 降序 小值. 如果child在右边, parent 比 child 小, parent才有效, 符合降序
			return cur.parent
		}
		cur = cur.parent
	}
	return nil
}

func (iter *Iterator) curPushNextStack(cur *Node) {
	next := cur.children[0] // 当前的左然后向右找, 找到最大, 就是最接近cur 并且小于cur的值

	if next != nil {
		iter.tstack.Push(next)
		for next.children[1] != nil {
			next = next.children[1]
			iter.tstack.Push(next) // 入栈 用于回溯
		}
	}
}

func (iter *Iterator) getPrevUp(cur *Node) *Node {
	for cur.parent != nil {
		if getRelationship(cur) == 0 { // Prev 在 降序 大值. 如果child在左边, parent 比 child 大, parent才有效 , 符合降序
			return cur.parent
		}
		cur = cur.parent
	}
	return nil
}

func (iter *Iterator) curPushPrevStack(cur *Node) {
	prev := cur.children[1]

	if prev != nil {
		iter.tstack.Push(prev)
		for prev.children[0] != nil {
			prev = prev.children[0]
			iter.tstack.Push(prev)
		}
	}
}