Solution.go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
type BSTIterator struct {
	stack []*TreeNode
}

func Constructor(root *TreeNode) BSTIterator {
	var stack []*TreeNode
	for ; root != nil; root = root.Left {
		stack = append(stack, root)
	}
	return BSTIterator{
		stack: stack,
	}
}

func (this *BSTIterator) Next() int {
	cur := this.stack[len(this.stack)-1]
	this.stack = this.stack[:len(this.stack)-1]
	for node := cur.Right; node != nil; node = node.Left {
		this.stack = append(this.stack, node)
	}
	return cur.Val
}

func (this *BSTIterator) HasNext() bool {
	return len(this.stack) > 0
}

/**
 * Your BSTIterator object will be instantiated and called as such:
 * obj := Constructor(root);
 * param_1 := obj.Next();
 * param_2 := obj.HasNext();
 */