How to Fix Maximum Subarray Errors

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

Fix maximum subarray errors when Kadane resets incorrectly or all-negative arrays produce wrong results.

Quick Fix

Wrong

def max_subarray(nums):
    m=c=0
    for n in nums:
        c+=n
        if c<0: c=0
        m=max(m,c)
    return m

Returns 0 for [-3,-2,-1] instead of -1.

Right

def max_subarray(nums):
    m=c=nums[0]
    for n in nums[1:]:
        c=max(n,c+n)
        m=max(m,c)
    return m

[-2,1,-3,4,-1,2,1,-5,4] -> 6 (subarray [4,-1,2,1]). O(n).

Prevention

Initialize with nums[0]. Use max(n,c+n) to decide fresh start or extend.

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