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

Step 1 : Sort the array in O(n logn)

Step 2 : Find two indices

0<=i

int i=0,j=n;
while(i k)
        j--;
}