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  1. Practice
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  3. Cracking the Coding Interview
  4. Trees: Is This a Binary Search Tree?
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Trees: Is This a Binary Search Tree?

  • valtheval + 2 comments

    Hi, I can't see why my solution is wrong, it looks pretty similar. If anyone has an idea...

    def check_binary_search_tree_(root):
    if (root is None):
        return True
    elif (root.left is None) and (root.right is None):
        return -float('inf')<root.data<float('inf')
    elif (root.left is None):
        return (root.right.data>root.data) and check_binary_search_tree_(root.right)
    elif (root.right is None):
        return (root.left.data<root.data) and check_binary_search_tree_(root.left)
    else:
        return (root.left.data<root.data) and (root.right.data>root.data) and check_binary_search_tree_(root.right) and check_binary_search_tree_(root.left)
    • condrint + 0 comments

      believe I had the same problem as you (our codes look similiar). So I reread the constraints of the problem and this bold part is important 'The data value of every node in a node's left subtree is less than the data value of that node.'

    • mindofmateo + 0 comments

      Hi, I know it's been three months since your comment, but I faced the same problem as you just now.

      The problem with your (our) approach is that it only checks the upper or lower bound for each side, respectively.

      Basically, there needs to be both an upper AND lower bound for each branch/node check. Some of the other submissions do this very well. This way all branches/nodes to the left are lower than the one above it, and all of the branches/nodes to the right are greater than the one above it.