How to Fix BST Validation Errors

In this tutorial, you'll learn about How to Fix BST Validation Errors. We cover key concepts, practical examples, and best practices.

Fix bst validation errors when only checking immediate children instead of full range constraints.

Quick Fix

Wrong

def val(r):
    if not r: return True
    if r.left and r.left.val>=r.val: return False
    if r.right and r.right.val<=r.val: return False
    return val(r.left) and val(r.right)

Only checks immediate children. Misses ancestor violations.

Right

def val(r):
    def ch(n,lo,hi):
        if not n: return True
        if lo is not None and n.val<=lo: return False
        if hi is not None and n.val>=hi: return False
        return ch(n.left,lo,n.val) and ch(n.right,n.val,hi)
    return ch(r,None,None)

[5,1,4,null,null,3,6] -> False. O(n).

Prevention

Pass min/max bounds. Left values < parent. Right values > parent.

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