leetCode---Intersection of Two Arrays

一. 题目：Intersection of Two Arrays

Intersection of Two Arrays I

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.

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思路分析：题目要求给定2个数组，找出交集，交集里没有重复元素，用set集合即可很方便的解决问题。

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

Intersection of Two Arrays II

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.

思路分析：题目要求给定2个数组，找出交集，此题跟上面题不太一样，可以有重复元素，用map集合即可很方便的解决问题。

class Solution {public:    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {        unordered_map<int,int> nmap;        vector<int> res;        for(int i = 0; i < nums1.size(); i++){            nmap[nums1[i]]++;        }        for(int i = 0; i < nums2.size(); i++){            if(nmap.find(nums2[i]) != nmap.end() && --nmap[nums2[i]] >= 0)                 res.push_back(nums2[i]);                        }        return res;    }};