Given an unsorted LaTeX: \texttt{vector} vector and a number LaTeX: n n , what is the worst-case time complexity for finding the pair of integers whose sum is closest to LaTeX: n n , if you are not allowed to use any additional memory? For example, if you were given the vector LaTeX: \{12, 3, 17, 5, 7\} { 12 , 3 , 17 , 5 , 7 } and LaTeX: n = 13 n = 13 , you would return the pair LaTeX: \{5, 7\} { 5 , 7 } .

Write a method named addall that could be placed inside the hashintset class. this method accepts another hashintset as a parameter and adds all elements from that set into the current set, if they are not already present. for example, if a set s1 contains [1, 2, 3] and another set s2 contains [1, 7, 3, 9], the call of s1.addall(s2); would change s1 to store [1, 2, 3, 7, 9] in some order. you are allowed to call methods on your set and/or the other set. do not modify the set passed in. this method should run in o(n) time where n is the number of elements in the parameter set passed in.