350. Intersection of Two Arrays II

Description

Given two arrays, write a function to compute their intersection.

Example: Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2].

Note:

• Each element in the result should appear as many times as it shows in both arrays.
• The result can be in any order.

Follow up:

• What if the given array is already sorted? How would you optimize your algorithm?
• What if nums1's size is small compared to nums2's size? Which algorithm is better?
• What if elements of nums2 are stored on disk, and the memory is limited such that you cannot load all elements into the memory at once?

Solution

/**
 * Solved with hash table
 * @param {number[]} nums1
 * @param {number[]} nums2
 * @return {number[]}
 */
var intersect = function(nums1, nums2) {
    "use strict";
    let table = {};
    let large = null, small = null;
    if (nums1.length > nums2.length) {
        large = nums1;
        small = nums2;
    } else {
        large = nums2;
        small = nums1;
    }
    for (let i = 0; i < large.length; i++) {
        if (table[large[i]] === undefined) {
            table[large[i]] = 0;
        }
        table[large[i]]++;
    }
    let result = [];
    for (let i = 0; i < small.length; i++) {
        if (table[small[i]]) {
            table[small[i]]--;
            result.push(small[i]);
        }
    }
    return result;
};