Find Sum To Match Target

find_sum.js

// find two numbers whose sum equals the target_sum value

function create_digits(numbers) {
  const digits = {};
  for (let i = 0; i < numbers.length; i++) {
    digits[numbers[i]] = 1;
  }
  return digits;
}

function find_sum(numbers, target_sum) {
  const digits = create_digits(numbers);
  for (let i = 0; i < numbers.length; i++) {
    const diff = target_sum - numbers[i];
    if (digits[diff]) {
      return [numbers[i], diff];
    }
  }
}

console.log(JSON.stringify(find_sum([1, 3, 8, 6, 2, 4, 7, 0], 10)) === JSON.stringify([3, 7]));
console.log(JSON.stringify(find_sum([1, 8, 8, 6, 2, 4, 7, 0], 10)) === JSON.stringify([8, 2]));
console.log(JSON.stringify(find_sum([1, 8, 8, 3, 2, 4, 7, 0], 10)) === JSON.stringify([8, 2]));
console.log(JSON.stringify(find_sum([-1, 11, 8, 3, 2, 4, 7, 0], 10)) === JSON.stringify([-1, 11]));
console.log(JSON.stringify(find_sum([], 10)) === undefined);
console.log(JSON.stringify(find_sum([1, 8, 8, 6, 2, 4, 7, 0], 100)) === undefined);

function find_sum_slow(numbers, target_sum) {
  for (let i = 0; i < numbers.length; i++) {
    for (let j = i + 1; j < numbers.length; j++) {
      if (numbers[i] + numbers[j] === target_sum) {
        return [numbers[i], numbers[j]];
      }
    }
  }
}