Code for solution of Udemy course.

TargetSumArray.java

import java.util.HashSet;
import java.util.Set;

/**
 * https://www.udemy.com/programming-code-interview/#/lecture/2519488 
 */
public class TargetSumArray {

    public static void main(String[] args) {
        TargetSumArray tsa = new TargetSumArray();
        int[] testArray = new int[]{9,5,2,7};
        int targetSum = 7;

        System.out.println("true is: "+ tsa.hasPairThatSumsTo(testArray, targetSum));

        targetSum = 11;
        System.out.println("true is: "+ tsa.hasPairThatSumsTo(testArray, targetSum));

        targetSum = 3;
        System.out.println("false is: "+ tsa.hasPairThatSumsTo(testArray, targetSum));

        testArray = new int[]{};
        System.out.println("false is: "+ tsa.hasPairThatSumsTo(testArray, targetSum));

        testArray = new int[]{1};
        System.out.println("false is: "+ tsa.hasPairThatSumsTo(testArray, targetSum));

    }

    public boolean hasPairThatSumsTo(int[] numbers, int targetSum ) {
        Set<Integer> lookupTable = new HashSet<>();

        for(int number: numbers) {
            int substraction = targetSum - number;

            if(lookupTable.isEmpty()) {
                lookupTable.add(substraction);
            } else {
                if (lookupTable.contains(number)) {
                    return true;
                } else {
                    lookupTable.add(substraction);
                }
            }
        }
        return false;
    }
}