How to Fix Dynamic Sliding Window Errors

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

Fix dynamic sliding window errors when window shrink condition wrong or left pointer not incrementing.

Quick Fix

Wrong

def dynamic(a,cond):
    l=mx=0; cur=0
    for r in range(len(a)):
        cur+=a[r]
        while cond(cur):
            cur-=a[l]; l+=1  # Wrong: if condition met, shrink
        mx=max(mx,r-l+1)
    return mx

Logic inverted: shrink when condition met, not when violated.

Right

def dynamic(a,target):
    l=0; cur=0; mx=0
    for r in range(len(a)):
        cur+=a[r]
        while cur>target:  # shrink when constraint violated
            cur-=a[l]; l+=1
        mx=max(mx,r-l+1)
    return mx

[4,2,1,3,5], target=6 -> 3 (subarray [4,2]... [2,1,3]), max length with sum <=6. O(n).

Prevention

Expand right pointer. While constraint violated, shrink from left. Track max window size.

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FAQ