350.intersection-of-two-arrays-ii.cpp

/*
 * @lc app=leetcode id=350 lang=cpp
 *
 * [350] Intersection of Two Arrays II
 *
 * https://leetcode.com/problems/intersection-of-two-arrays-ii/description/
 *
 * algorithms
 * Easy (48.18%)
 * Total Accepted:    212.1K
 * Total Submissions: 440.1K
 * Testcase Example:  '[1,2,2,1]\n[2,2]'
 *
 * Given two arrays, write a function to compute their intersection.
 * 
 * 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]
 * 
 * 
 * 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?
 * 
 * 
 */
#include<bits/stdc++.h>
using namespace std;

class Solution {
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {

    unordered_map<int, int> mm;
    vector<int> ans;
    
    for(auto e: nums1)
        mm[e]++;
    for(auto e: nums2){
        mm[e]--;
        if(mm[e]>=0)
            ans.push_back(e);
    }
    return ans;
    }
};