15 lines
412 B
Python
15 lines
412 B
Python
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def is_valid(node):
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"""
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Return True if `node` is a valid binary search tree.
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"""
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s = []
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s.append((float('-inf'), node, float('inf')))
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while s:
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lo, node, hi = s.pop()
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if lo <= node.value <= hi:
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node.lhs and s.append((lo, node.lhs, node.value))
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node.rhs and s.append((node.value, node.rhs, hi))
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else:
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return False
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return True
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