checking if 2 numbers of array add up to I

Question

I saw a interview question as follows: Give an unsorted array of integers A and and an integer I, find out if any two members of A add up to I.

any clues?

ti

Answer 1

An implementation in python

def func(list,k):
temp={} ## temporary dictionary
for i in range(len(list)):
    if(list[i] in temp): ## if temp already has the key just increment its value
        temp[list[i]] +=1
    else:  ## else initialize the key in temp with count as 0
        temp[list[i]]=0 

    if(k-list[i] in temp and ((k/2 != list[i]) or temp[list[i]]>=1)): ## if the corresponding other value to make the sum k is in the dictionary and its either not k/2 or the count for that number is more than 1
        return True

return False

Input: list is a list of numbers (A in the question above)...
k is the sum (I in the question above)....

The function outputs True if there exist a pair in the list whose sum is equal to k and False otherwise...

I am using a dictionary whose key is the element in the array(list) and value is the count of that element(number of times that element is present in that list). Average running time complexity is O(n).

This implementation also takes care of two important edge cases:

• repeated numbers in the list and
• not adding the same number twice.