How to Fix BST Deletion Errors

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

Fix bst deletion errors when three-case logic fails on two-child nodes or successor management wrong.

Quick Fix

Wrong

def del(r,v):
    if not r: return None
    if v<r.val: r.left=del(r.left,v)
    elif v>r.val: r.right=del(r.right,v)
    else:
        if not r.left: return r.right
        if not r.right: return r.left
        s=r.right
        while s.left: s=s.left
        r.val=s.val
        r.right=del(r.right,s.val)
    return r

Correct version shown. Common mistake: forgetting to delete successor.

Right

def del(r,v):
    if not r: return None
    if v<r.val: r.left=del(r.left,v)
    elif v>r.val: r.right=del(r.right,v)
    else:
        if not r.left: return r.right
        if not r.right: return r.left
        s=r.right
        while s.left: s=s.left
        r.val=s.val
        r.right=del(r.right,s.val)
    return r

Delete 5 from [5,3,7,2,4,6,8] -> new root 6. O(log n) avg.

Prevention

Three cases: no child (return None), one child (return child), two children (replace with successor).

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FAQ