How to Fix Range Sum in BST Errors

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

Fix range sum in bst errors when pruning misses valid branches or range boundaries are exclusive.

Quick Fix

Wrong

def sum(r,lo,hi):
    if not r: return 0
    s=r.val if lo<=r.val<=hi else 0
    return s+sum(r.left,lo,hi)+sum(r.right,lo,hi)

No pruning. Visits all nodes even when subtree out of range.

Right

def sum(r,lo,hi):
    if not r: return 0
    if r.val<lo: return sum(r.right,lo,hi)
    if r.val>hi: return sum(r.left,lo,hi)
    return r.val+sum(r.left,lo,hi)+sum(r.right,lo,hi)

[10,5,15,3,7,null,18], lo=7, hi=15 -> 32 (10+7+15). O(n) worst, O(log n) with pruning.

Prevention

Prune left when root.val < lo. Prune right when root.val > hi.

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