Leetcode-349 Intersection of Two Arrays

题目介绍

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库提供两个散列集合类unordered_set和unordered_multiset,STLport也提供hash_set和hash_multiset，它们的接口，用法与stl里的标准关联容器set/multiset相同，只是内部使用散列表代替了二叉树实现，因此查找复杂度由数降为常数。

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;
    }
};