350. Intersection of Two Arrays II

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?

AC code:

class Solution {
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
        vector<int> ans;
        vector<int> temp;
        int len1 = nums1.size();
        int len2 = nums2.size();
        if (len1 == 0 || len2 == 0) return ans;
        sort(nums1.begin(), nums1.end());
        sort(nums2.begin(), nums2.end());
        for (int i = 0, j = 0; i < len1 && j < len2; ) {
            if (nums1[i] < nums2[j]) i++;
            else if (nums1[i] > nums2[j]) j++;
            else {
                ans.push_back(nums1[i]);
                i++, j++;
            }
        }
        return ans;
    }
};