# #  # @param root TreeNode类  # @return int整型一维数组 # class Solution:     def preorderTraversal(self , root ):         # write code here         reList = []         if root is None:             return reList         stack = []         node = root         while node is not None:             if  isinstance(node.val, int):                 reList.append(node.val)             if node.right is not None:                 stack.append(node.right)             node = node.left             if node is None and len(stack)>0:                 node = stack.pop(-1)         return reList

前序遍历的迭代算法关键在于：设置一个栈，每次将节点的右孩子压入栈中，当遍历完根节点和左子树，便从栈中弹出右子树，继续循环深入