Problem

Given a list of integers and a target sum, determine whether any two integers in the list sum to the target sum.
Example input: [1, 2, 3, 4, 5], target sum = 9
Example output: true (because 4 + 5 = 9)

Solution

// Solution:
// This solution is optimal because it uses a hash table to store the values of the array.
// This allows us to check if the complement of the current value is in the hash table.
// If it is, then we have found a pair that sums to the target sum.
// This solution is O(n) time complexity and O(n) space complexity.

function twoSum(arr, target) {
  const hash = {};
  for (let i = 0; i < arr.length; i++) {
    const complement = target - arr[i];
    if (hash[complement]) {
      return true;
    }
    hash[arr[i]] = true;
  }
  return false;
}

console.log(twoSum([1, 2, 3, 4, 5], 9)); // true
console.log(twoSum([1, 2, 3, 4, 5], 10)); // false