How to Fix Two Sum Array Errors

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

Fix two sum array errors when hash map lookups fail causing O(n^2) brute force timeouts.

Quick Fix

Wrong

def two_sum(nums, target):
    for i in range(len(nums)):
        for j in range(len(nums)):
            if i != j and nums[i]+nums[j]==target:
                return [i,j]

O(n^2) brute force fails large inputs.

Right

def two_sum(nums, target):
    seen={}
    for i,n in enumerate(nums):
        diff=target-n
        if diff in seen: return [seen[diff],i]
        seen[n]=i

Input: [2,7,11,15], 9 -> [0,1]. O(n).

Prevention

Use hash map for O(1) lookups. Check complement before storing current element.

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