Arrays in JS- Intersection Of Two Arrays

Problem Statement

Given two arrays, write a function to compute their intersection.The result can be in any order. Each element in the result should be unique

Here is the LeetCode link to the problem: 349. Intersection of Two Arrays

Runtime for this solution is 52 ms.

Test Cases:

Example 1:

Input: nums1 = [1,2,2,1], nums2 = [2,2]

Output: [2]

Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]

Output: [9,4]

Code

/**
* @param {number[]} nums1
* @param {number[]} nums2
* @return {number[]}
*/
var intersection = function(nums1, nums2) {

    let arr = [];

    let arr1 = [...new Set(nums1)];
    let arr2 = [...new Set(nums2)];

    const len1 = arr1.length;
    const len2 = arr2.length;

    if(len1 > len2){
        arr1.map((el) => {
            if(arr2.includes(el)){
                arr.push(el)
            }
        })
    }else{
        arr2.map((el) => {
            if(arr1.includes(el)){
                arr.push(el)
            }
        })
    }

    return arr;
};

Other Problems

Now let’s tweak the other problem a bit. Instead of Each element in the result should be unique we now add a condition where Each element in the result should appear as many times as it shows in both arrays.

Here is the LeetCode link to the above problem: 350. Intersection of Two Arrays II

Let’s look at some test cases for this:

Test Cases:

Example 1:

Input: nums1 = [1,2,2,1], nums2 = [2,2]

Output: [2,2]

Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]

Output: [4,9]

Solution1

/**
* @param {number[]} nums1
* @param {number[]} nums2
* @return {number[]}
*/
let sortFunction = (a,b) => a-b;
var intersect = function(nums1, nums2) {
    let a1 = nums1.sort(sortFunction);
    let a2 = nums2.sort(sortFunction);
    let intersection = [];

    while(a1.length && a2.length){
        if(a1[0] === a2[0]){
            intersection.push(a1.shift());
            a2.shift();
        } 
        else if(a1[0] > a2[0]){
            a2.shift();
        }else{
            a1.shift();
        }
    }

    return intersection;
};

Solution2

var intersect = function(nums1, nums2) {

    if(nums1.length === 0) return nums1;
    if(nums2.length === 0) return nums2;


    if(nums1.length > nums2.length){
        return intersect(nums2,nums1);
    }

    const obj = nums1.reduce((acc, el) => {
        return acc.set(el, acc.get(el) && (acc.get(el) + 1) || 1);
    }, new Map());

    return nums2.filter(i => {
        return obj.get(i) ? obj.set(i, obj.get(i) - 1) || true : false;
    });
};