Problem
Given two arrays, write a function to compute their intersection.
Example:
Given nums1 = [1, 2, 2, 1]
, nums2 = [2, 2]
, return [2, 2]
.
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?
Solution1: Hashtable
Time complexity: O(m + n)
Space complexity: O(m)
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// Author: Huahua // Running time: 4 ms class Solution { public: vector<int> intersect(vector<int>& nums1, vector<int>& nums2) { unordered_map<int, int> count; vector<int> ans; for (int num : nums1) ++count[num]; for (int num : nums2) if (count.count(num) &&count[num] > 0) { --count[num]; ans.push_back(num); } return ans; } }; |