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?
Example 2:
Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4] Output: [4,9]
A:
class Solution { public: vector<int> intersect(vector<int>& nums1, vector<int>& nums2) { map<int,int> m1; for(auto v : nums1) { if(m1.find(v) == m1.end()) { m1.insert({v,1}); }else{ auto it = m1.find(v); it->second += 1; } } vector<int> res; for(auto v : nums2) { auto it = m1.find(v); if( it != m1.end()) { res.push_back(v); it->second -= 1; if(it->second == 0) { m1.erase(v); } } } return res; } };
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