Intersection of Two Arrays II Solutions in C++

// Source : https://leetcode.com/problems/intersection-of-two-arrays-ii/
// Author : Calinescu Valentin, Hao Chen
// Date   : 2016-05-22


 
 /* Solution
  * --------
  *
  * Follow up:
  * 
  * 1)If the given array is already sorted we can skip the sorting.
  * 
  * 2)If nums1 is significantly smaller than nums2 we can only sort nums1 and then binary
  * search every element of nums2 in nums1 with a total complexity of (MlogN) or if nums2
  * is already sorted we can search every element of nums1 in nums2 in O(NlogM)
  *
  * 3)Just like 2), we can search for every element in nums2, thus having an online
  * algorithm.
  */
  
class Solution { // O(NlogN + MlogM)
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
        sort(nums1.begin(), nums1.end());//we sort both vectors in order to intersect
        sort(nums2.begin(), nums2.end());//them later in O(N + M), where N = nums1.size()
        vector <int> solution;                                         //M = nums2.size() 
        int index = 0;
        bool finished = false;
        for(int i = 0; i < nums1.size() && !finished; i++)
        {
            while(index < nums2.size() && nums1[i] > nums2[index])//we skip over the
                index++;//smaller elements in nums2
            if(index == nums2.size())//we have reached the end of nums2 so we have no more
                finished = true;//elements to add to the intersection
            else if(nums1[i] == nums2[index])//we found a common element
            {
                solution.push_back(nums1[i]);
                index++;
            }
        }
        return solution;
    }
};



/*
 * Just simply use the map can have O(M+N) time complexity.
 *
 */


class Solution {
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
        unordered_map<int, int> m;
        for (auto n: nums1) {
            m[n]++;
        }
        vector<int> result;
        for (auto n:nums2){
            if (m.find(n) != m.end() && m[n]>0 ){
                result.push_back(n);
                m[n]--;
            }                    
        }
        return result;
    }
};

/// Source : https://leetcode.com/problems/intersection-of-two-arrays-ii/description/
/// Author : liuyubobobo
/// Time   : 2017-11-14

#include <iostream>
#include <vector>
#include <unordered_map>
using namespace std;


/// Using Hash Map
/// Time Complexity: O(len(nums1) + len(nums2))
/// Space Complexity: O(len(nums1))
class Solution {
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {

        unordered_map<int, int> record;
        for(int i = 0 ; i < nums1.size() ; i ++)
            record[nums1[i]] += 1;

        vector<int> resultVector;
        for(int i = 0 ; i < nums2.size() ; i ++)
            if(record[nums2[i]] > 0){
                resultVector.push_back(nums2[i]);
                record[nums2[i]] --;
            }

        return resultVector;
    }
};


void print_vec(const vector<int>& vec){
    for(int e: vec)
        cout << e << " ";
    cout << endl;
}

int main() {

    vector<int> nums1 = {1, 2, 2, 1};
    vector<int> nums2 = {2, 2};

    print_vec(Solution().intersect(nums1, nums2));

    return 0;
}

/// Source : https://leetcode.com/problems/intersection-of-two-arrays-ii/description/
/// Author : liuyubobobo
/// Time   : 2017-11-14

#include <iostream>
#include <vector>
#include <set>

using namespace std;


/// Using Hash Map
/// Time Complexity: O(len(nums1) + len(nums2)*log(len(nums1)))
/// Space Complexity: O(len(nums1))
class Solution {
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {

        multiset<int> record;
        for(int num: nums1)
            record.insert(num);

        multiseSt<int> result;
        for(int num: nums2){
            multiset<int>::iterator iter = record.find(num);
            if( iter != record.end()){
                result.insert(num);
                record.erase(iter);
            }
        }

        return vector<int>(result.begin(), result.end());
    }
};


void print_vec(const vector<int>& vec){
    for(int e: vec)
        cout << e << " ";
    cout << endl;
}

int main() {

    vector<int> nums1 = {1, 2, 2, 1};
    vector<int> nums2 = {2, 2};

    print_vec(Solution().intersect(nums1, nums2));

    return 0;
}

/// Source : https://leetcode.com/problems/intersection-of-two-arrays-ii/description/
/// Author : liuyubobobo
/// Time   : 2019-04-08

#include <iostream>
#include <vector>
#include <set>

using namespace std;


/// Sorting and Two Pointers
/// Time Complexity: O(nlogn)
/// Space Complexity: O(1)
class Solution {
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {

        sort(nums1.begin(), nums1.end());
        sort(nums2.begin(), nums2.end());

        vector<int> res;

        int i = 0, j = 0;
        while(i < nums1.size() && j < nums2.size()){

            if(nums1[i] == nums2[j]) res.push_back(nums1[i]), i ++, j ++;
            else if(nums1[i] < nums2[j]) i ++;
            else j ++;
        }

        return res;
    }
};


void print_vec(const vector<int>& vec){
    for(int e: vec)
        cout << e << " ";
    cout << endl;
}

int main() {

    vector<int> nums1 = {1, 2, 2, 1};
    vector<int> nums2 = {2, 2};

    print_vec(Solution().intersect(nums1, nums2));

    return 0;
}