Algorythms

numPairEqualSum.js

// Given an array of numbers as an argument, and a number as a second argument
// find two numbers in the array that adds up the sum.
// const array = [2, 8, -19, 33, 923];
// const sum = 904;
// returns [-19, 923]

/**
 * Function that searches for a pair of numbers which add up to the given sum
 * @param array | Array<number>
 * @param sum | number
 * @returns Array<number>
 */
const numPairEqualSum = (array, sum) => {
  // create a lookup set to store numbers of the array while looping over the array that may add up to the sum
  // as the subsequent number is evaluated in the loop
  let set = new Set();
  
  // let's loop over the array and check if we have seen the complementary number we stored in the set
  for (let i = 0; i < array.length; i++) {
    if (set.has(sum - array[i])) {
      return [(sum - array[i]), array[i]];
    }
    
    // if the number at the current index is not adding up to a number in the set we'll add it to the set
    set.add(array[i]);
  }
  
  // if not two numbers add up to the sum, then return an empty array.
  return [];
}

// time complexity: O(n)
// space complexity: O(n)