https://leetcode.com/problems/binary-tree-inorder-traversal/ Swift solution

binary_tree_inorder_traversal.swift

// https://leetcode.com/problems/binary-tree-inorder-traversal/
class TreeNode{
    let val:Int
    var left:TreeNode?
    var right:TreeNode?
    init(val:Int){
        self.val = val
    }
}

func inorderTraversal(rootTreeNode:TreeNode) -> [Int]{
    var nodeList = [TreeNode]()
    var arr = [Int]()
    var current:TreeNode = rootTreeNode
    nodeList.append(rootTreeNode)
    while(!nodeList.isEmpty ){
        // 一直向左走 move to left
        while(current.left != nil){
            nodeList.append(current.left!)
            current = current.left!
        }
        // no way ,backforward
        let left = nodeList.removeLast()
        arr.append(left.val)
        // turn right a step
        if let right = left.right{
            current = right
            nodeList.append(right)
        }
    }
    return arr
    
}