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Challenge: Array Intersection

Instructions

Write a function called arrayIntersection that takes in two arrays and returns an array containing the intersection of the two input arrays (i.e., the common elements that appear in both arrays).

Function Signature

/**
 * Returns the intersection of two arrays.
 * @param {number[]} arr1 - The first array.
 * @param {number[]} arr2 - The second array.
 * @returns {number[]} - The intersection of the two arrays.
 */
function arrayIntersection(arr1: number[], arr2: number[]): number[];

Examples

arrayIntersection([1, 2, 3, 4, 5], [1, 3, 5, 7, 9]); // should return [1, 3, 5]
arrayIntersection([1, 1, 1, 1, 1], [2, 2, 2, 2, 2]); // should return []
arrayIntersection([1, 2, 3, 4, 5], [5, 4, 3, 2, 1]); // should return [1, 2, 3, 4, 5]

Constraints

  • The input arrays can contain any number of elements
  • The input arrays can contain any positive integer

Hints

  • You could use a for loop to iterate through the first array and check if each element is in the second array using the includes method.
  • You could also take the approach of using a Set to store the elements of the first array and then iterate through the second array and check if each element is in the Set using the has method.

Solutions

Click For Solution 1 
function arrayIntersection(arr1, arr2) {
  const intersection = [];

  for (let i = 0; i < arr1.length; i++) {
    if (arr2.includes(arr1[i]) && !intersection.includes(arr1[i])) {
      intersection.push(arr1[i]);
    }
  }

  return intersection;
}

Explanation

  • Iterate through the first array
  • For each element, check if it is in the second array using the includes method
  • If it is, check if it is already in the intersection array using the includes method
  • If it is not, push it into the intersection array
  • Return the intersection array
Click For Solution 2

In this solution, we will use a Set. A Set is a data structure that stores unique values. We will have a section on maps, sets later. If you are not familiar with sets, that is fine. You can still follow along with this solution.

function arrayIntersection(arr1, arr2) {
  const set1 = new Set(arr1);
  const intersection = [];

  for (let num of arr2) {
    if (set1.has(num)) {
      intersection.push(num);
    }
  }

  return intersection;
}

Explanation

  • Create a new Set from the first array
  • Iterate through the second array and check if each element is in the set using the has method
  • If it is, push it into the intersection array
  • Return the intersection array

Test Cases

test('Finding array intersection', () => {
  expect(arrayIntersection([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])).toEqual([
    3, 4, 5,
  ]);
  expect(arrayIntersection([10, 20, 30], [30, 40, 50])).toEqual([30]);
  expect(arrayIntersection([1, 2, 3], [4, 5, 6])).toEqual([]);
});