LeetCode 350. Intersection of Two Arrays II

Posted 2020-08-09

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?

 

 

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和349题类似，只要稍作改动即可

 

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

        }
        return ret;
    }
};