class Node:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.righ = None


def preorder_print(node):
    if node == None:
        return
    print(node.value, end=' ')
    preorder_print(node.left)
    preorder_print(node.right)


def arr2tree(arr):
    N = len(arr)
    
    for i in range(N):
        arr[i] = Node(arr[i])

    for i in range(N):
        arr[i].left = None if (i*2 + 1 >= N) else arr[i*2 + 1]
        arr[i].right = None if (i*2 + 2 >= N) else arr[i*2 + 2]

    return arr[0]


if __name__ == '__main__':
    arr = [1, 2, 3, 4, 5, 6, 7]
    root = arr2tree(arr)
    preorder_print(root)

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