Is this an O(N) solution? I'm being told this is O(N^2) because of the in keyword

Question

I believe the code below is an O(N) solution but I'm being told it is O(N^2) because of the in keyword. Is that true?

Code:

class Solution:
    def twoSum(self, nums, target):
        for i,v in enumerate(nums):
            value = target - v
            if value in nums and nums.index(value)!= I:
                return (nums.index(value),I)
                break

Answer 1

x in a_list is O(n) as is nums.index(value) ... so your inner if statement is O(2n) and your outer for loop is O(n)

so you have O(n)*O(2n) = O(2n^2) = O(n^2)

the O(n) solution is as follows

def twoSum(x,targetValue):
    # pending values is a dict of index's mapped where the key is key + x[pendingValues[key]] = targetValue
    pendingValues = {}
    for i,value in enumerate(x):
        if value in pendingValues: # in Dict is only O(1)
           # this is a match return both matching index's
           return (pendingValues[value],i)
        else:
           # not a match store the index as matchedTarget=index
           pendingValues[targetValue-value] = i