https://leetcode.com/problems/inorder-successor-in-bst/

inorder-successor-in-bst.go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func inorderSuccessor(root *TreeNode, p *TreeNode) *TreeNode {
    if root == nil || p == nil {
        return nil
    }
    
    return inorder(root, p)
}

func inorder(root, p *TreeNode) *TreeNode {
    stack := []*TreeNode{}
    target := (1 << 31) - 1
    
    for root != nil || len(stack) > 0 {
        for root != nil {
            stack = append(stack, root)
            root = root.Left
        }
        
        root = stack[len(stack) - 1] 
        stack = stack[:len(stack) - 1]
        
        if target == p.Val {
            return root
        }

        target = root.Val
        root = root.Right
    }
    
    return nil
}