How to Fix Sliding Window Maximum Errors

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

Fix sliding window maximum errors when deque fails to remove out-of-window elements or monotonic order lost.

Quick Fix

Wrong

def max_sliding(n,k):
    return [max(n[i:i+k]) for i in range(len(n)-k+1)]

O(n*k) brute force times out.

Right

from collections import deque
def max_sliding(n,k):
    dq=deque(); r=[]
    for i,v in enumerate(n):
        while dq and n[dq[-1]]<v: dq.pop()
        dq.append(i)
        if dq[0]<=i-k: dq.popleft()
        if i>=k-1: r.append(n[dq[0]])
    return r

[1,3,-1,-3,5,3,6,7], k=3 -> [3,3,5,5,6,7]. O(n).

Prevention

Deque stores indices in decreasing value. Remove front if out of window.

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