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

Creating a hash table and then looking for value in it.

function sum_exist(num : number, arr : any[]) {
    var number_seen = {};
    for(let item of arr){
        if(num - item in number_seen){
            return true
        }
        number_seen[item] = 0;
    }
    return false;
}

Test case (using Jest)

test('Given a list of numbers, return whether any two sums equal to the set number.', () => {
    expect(sum_exist(17 , [10, 15, 3, 7])).toEqual(true);
});


test('Given a list of numbers, return whether any two sums equal to the set number.', () => {
    expect(sum_exist(16 , [10, 15, 3, 7])).toEqual(false);
});

Answer 2

@Test
public void hasPairWithSum() {
  assertFalse(hasPairWithSum_Ordered_Logarithmic(new int[] { 1, 2, 3, 9 }, 8));
  assertTrue(hasPairWithSum_Ordered_Logarithmic(new int[] { 1, 2, 4, 4 }, 8));

  assertFalse(hasPairWithSum_Ordered_Linear(new int[] { 1, 2, 3, 9 }, 8));
  assertTrue(hasPairWithSum_Ordered_Linear(new int[] { 1, 2, 4, 4 }, 8));

  assertFalse(hasPairWithSum_Unsorted_Linear(new int[] { 9, 1, 3, 2 }, 8));
  assertTrue(hasPairWithSum_Unsorted_Linear(new int[] { 4, 2, 1, 4 }, 8));

  assertFalse(hasPairWithSum_Unsorted_Quadratic(new int[] { 9, 1, 3, 2 }, 8));
  assertTrue(hasPairWithSum_Unsorted_Quadratic(new int[] { 4, 2, 1, 4 }, 8));
}

private boolean hasPairWithSum_Ordered_Logarithmic(int[] data, int sum) {
  for (int i = 0; i < data.length; i++) {
    int current = data[i];
    int complement = sum - current;
    int foundIndex = Arrays.binarySearch(data, complement);
    if (foundIndex >= 0 && foundIndex != i) {
      return true;
    }
  }
  return false;
}

private boolean hasPairWithSum_Ordered_Linear(int[] data, int sum) {
  int low = 0;
  int high = data.length - 1;
  while (low < high) {
    int total = data[low] + data[high];
    if (total == sum) {
      return true;
    } else if (total < sum) {
      low++;
    } else {
      high--;
    }
  }
  return false;
}

private boolean hasPairWithSum_Unsorted_Linear(int[] data, int sum) {
  Set<Integer> complements = Sets.newHashSet();
  for (int current : data) {
    if (complements.contains(current)) {
      return true;
    }
    complements.add(sum - current);
  }
  return false;
}

private boolean hasPairWithSum_Unsorted_Quadratic(int[] data, int sum) {
  for (int i = 0; i < data.length; i++) {
    int current = data[i];
    int complement = sum - current;
    for (int j = 0; j < data.length; j++) {
      if (data[j] == complement && i != j) {
        return true;
      }
    }
  }
  return false;
}

Answer 3

We can use C++ STL map to solve this

void subsetSum(int arr[], int n, int sum)
{
    map<int, int>Map;

    for(int i=0; i<n; i++)
    {
        Map[arr[i]]++;
        if(Map.count(sum-arr[i]))
        {
            cout<<arr[i]<<" "<<sum-arr[i]<<"\n";
        }
    }
}