https://leetcode.cn/problems/uncommon-words-from-two-sentences/


class Solution {
public:
    vector<string> uncommonFromSentences(string s1, string s2) {
        // 将两个语句拼接
        string s = s1 + " " + s2;
        
        // 分离单词
        vector<string> vRet;
        string temp;
        for(size_t i = 0; i < s.size(); ++i)
        {
            if(s[i] != ' ')
            {
                temp += s[i];
            }
            else
            {
                vRet.push_back(temp);
                temp.clear();
            }
        }
        if(!temp.empty())
        {
            vRet.push_back(temp);
        }
 
        // 统计每个单词出现的次数
        unordered_map<string, int> m;
        for(auto e : vRet)
            m[e]++;
        
        vRet.clear();
 
        // 将出现一次的单词保存在vRet中
        for(auto e : m)
        {
            if(e.second == 1)
                vRet.push_back(e.first);
        }
 
        return vRet;
    }
};


https://leetcode.cn/problems/intersection-of-two-arrays-ii/submissions/

class Solution {
public:
    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
        //记录每个数出现的次数
        unordered_map<int, int> m;
        for(auto v1:nums1)
        {
            m[v1]++;
        }

        //取交集
        vector<int> v;
        
        for (int num : nums2) {
            if (m.count(num)) {
                v.push_back(num);
                --m[num];
                if (m[num] == 0) {
                    m.erase(num);
                }
            }
        }


        return v;
    }
};

https://leetcode.cn/problems/n-repeated-element-in-size-2n-array/

class Solution {
public:
    int repeatedNTimes(vector<int>& nums) {
        unordered_map<int, int> umap;   
        for(auto v:nums)
        {
            umap[v]++;  //统计一下，每种元素出现的个数。
        }

        //遍历一遍, 找出来重复n次的元素
        int ret=0;
        for(auto e:umap)
        {
            if(2*e.second==nums.size())
            {
                ret= e.first;
                break;
            }
        }

        return ret;
    }
};

https://leetcode.cn/problems/intersection-of-two-arrays/submissions/
class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        //思路：先利用set去重；然后比较，小的要先走-相等的存起来并一起走。
        set<int> s1(nums1.begin(), nums1.end());
        set<int> s2(nums2.begin(), nums2.end());

        vector<int> v;
        set<int, int>::iterator it1=s1.begin();
        set<int, int>::iterator it2=s2.begin();
        while(it1 != s1.end() && it2 != s2.end())
        {
            if(*it1 < *it2)
            {
                ++it1;
            }
            else if(*it1 > *it2)
            {
                ++it2;
            }
            else
            {
                v.push_back(*it1);
                ++it1;
                ++it2;
            }
        }

        return v;
    }
};