Untitled

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


def build_tree(s):
    s = s[1:-1].split(',')
    if len(s) == 0:
        return
    nodes = [('root', s[0])]
    for i, c in enumerate(s[1:]):
        if c != 'null':
            if i & 1:
                nodes.append((nodes[i // 2][0] + '.right', c))
            else:
                nodes.append((nodes[i // 2][0] + '.left', c))
    for node in nodes:
        print(node[0] + ' = TreeNode(' + node[1] + ')')