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class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

def inorder_iterative(root):
    stack = []
    curr = root

    while curr or stack:
        while curr:
            stack.append(curr)
            curr = curr.left

        curr = stack.pop()
        print(curr.val, end=" ")

        curr = curr.right