Leetcode-349 Intersection of Two Arrays

題目介紹

Given two arrays, write a function to compute their intersection.

Example:
Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2].

Note:
Each element in the result must be unique.
The result can be in any order.

C++ 解法 using unordered_set

unordered庫提供兩個散列集合類unordered_set和unordered_multiset,STLport也提供hash_set和hash_multiset，它們的接口，用法與stl裏的標準關聯容器set/multiset相同，只是內部使用散列表代替了二叉樹實現，因此查找複雜度由數降爲常數。

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        unordered_set<int> m(nums1.begin(), nums1.end());
        vector<int> res;
        for (auto a : nums2)
            if (m.count(a)) {
                res.push_back(a);
                m.erase(a);
            }
        return res;
    }
};