readme.md

Challenge: Find Pair Sum

You are given an array of integers and a target sum. Implement a function called findPairSum that finds and returns a pair of distinct elements from the array whose sum is equal to the target sum. If no such pair exists, return null. You should use the DoublyLinkedList class/constructor to efficiently implement this function.

Function Signature

/**
 * Finds a pair of distinct elements from the array whose sum is equal to the target sum.
 * @param {number[]} nums - The array of integers.
 * @param {number} targetSum - The target sum to find.
 * @returns {number[] | null} - An array containing the pair of elements whose sum is the target sum, or null if no such pair exists.
 */
function findPairSum(nums: number[], targetSum: number): number[] | null

Example

const nums = [2, 6, 3, 8, 10, 5];
const targetSum = 12;

const pair = findPairSum(nums, targetSum);
console.log(pair); // Should print: [2, 10]

Hints

• Create a DoublyLinkedList to store the encountered numbers.
• For each number in the array, calculate the difference between the target sum and the current number.
• Check if the calculated difference exists in the DoublyLinkedList. If it does, you found a pair.

Solution

Click to reveal solution

function findPairSum(nums, targetSum) {
  const seen = new DoublyLinkedList();

  for (const num of nums) {
    const difference = targetSum - num;
    if (seen.contains(difference)) {
      return [difference, num];
    }
    seen.append(num);
  }

  return null;
}

• Instantiate a new DoublyLinkedList called seen to store the encountered numbers.
• Iterate through the input array nums using a for...of loop.
• For each number num in the array, calculate the difference between the target sum and the current number. Store the difference in a variable called difference.
• Check if the seen list contains the difference. If it does, return an array containing the difference and num.
• Otherwise, append the num to the seen list.
• If no such pair exists, return null.

Test Cases

describe('findPair', () => {
  it('should find a pair with the given target sum', () => {
    const nums = [2, 6, 3, 8, 10, 5];
    const targetSum = 12;
    const pair = findPair(nums, targetSum);
    expect(pair).toEqual([2, 10]);
  });

  it('should return null if no such pair exists', () => {
    const nums = [1, 2, 3, 4, 5];
    const targetSum = 10;
    const pair = findPair(nums, targetSum);
    expect(pair).toBeNull();
  });
});