Find all pairs of integers within an array which sum to a specified value

Question

Design an algorithm to find all pairs of integers within an array which sum to a specified value.

I have tried this problem using a hash

Answer 1

You don't even need to store all the elements in hashmap, and then scan. You can scan during the first iteration itself.

void foo(int[] A, int sum) {
    HashSet set = new HashSet();
    for (int e : A) {
        if (set.contains(sum-e)) {
            System.out.println(e + "," + (sum-e));
            // deal with the duplicated case
            set.remove(sum-e);
        } else {
            set.add(e);
        }
    }
}