How to write an algorithm to check if the sum of any two numbers in an array/list matches a given number?

Question

How can I write an algorithm to check if the sum of any two numbers in an array/list matches a given number with a complexity of nlogn?

Answer 1

This is in Java : This even removes the possible duplicates.. Runtime - O(n^2)

private static int[] intArray = {15,5,10,20,25,30};
private static int sum = 35;

private static void algorithm()
{
    Map intMap = new Hashtable();
    for (int i=0; i