2021-09-17 Daily-Challenge

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In: DailyChallenge

Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 17

Description

Intersection of Two Arrays II

Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must appear as many times as it shows in both arrays and you may return the result in any order.

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]
Explanation: [9,4] is also accepted.

Constraints:

  • 1 <= nums1.length, nums2.length <= 1000
  • 0 <= nums1[i], nums2[i] <= 1000

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

class Solution {
public:
  vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
    sort(nums1.begin(), nums1.end());
    sort(nums2.begin(), nums2.end());

    vector<int> answer;
    auto it1 = nums1.begin();
    auto it2 = nums2.begin();
    while(it1 != nums1.end() && it2 != nums2.end()) {
      if(*it1 == *it2) {
        answer.push_back(*it1);
        ++it1;
        ++it2;
      } else if(*it1 < *it2) {
        ++it1;
      } else {
        ++it2;
      }
    }

    return answer;
  }
};

// Accepted
// 55/55 cases passed (3 ms)
// Your runtime beats 91.05 % of cpp submissions
// Your memory usage beats 88.6 % of cpp submissions (9.9 MB)
Algorithm