查找三个数组的公共元素

 #include <iostream>
 #include <vector>
 #include <unordered_set>
 
 using std::cout;
 using std::endl;
 using std::cin;
 using std::vector;
 using std::unordered_set;
 
 //因为set比数组占用的空间大，并且set把数值映射到key都要做hash计算，速度也比数组慢
 //如果数组数值范围可控可以使用数组做hash
 const int M = 20;   //数值的范围
 vector<int> getIntersection3(const vector<int>& nums1, const vector<int>& nums2) {
     unordered_set<int> result_set;  //给结果去重
     int hashTable[M] = {0};
     for(int num : nums1) {
         hashTable[num] = 1;
     }
 
     for(int num : nums2) {
         if(hashTable[num] == 1) {
             result_set.insert(num);
         }
     }
     return vector(result_set.begin(), result_set.end());
 }
 
  void print(const vector<int>& vec) {
     for(int i : vec) {
         cout << i << ' ';
     }
     cout << endl;
 }
 
int main() {
       vector<int> v1 = { 1,2,2,3,4,5,5,5,8,9,11,13 };
       vector<int> v2 = { 2,2,2,3,5,6,7,7,8,9,10,12,12,13,13,14 };
       vector<int> v3 = { 1,1,1,2,2,4,5,6,7,7,8,9,10,14,14,17,18,20 };
       //print(v1);
       //print(v2);
   
       //vector<int> ret = getIntersection(v1, v2);
       //print(ret);
       //vector<int> ret2 = getIntersection2(v1, v2);
       //print(ret2);
       //vector<int> ret3 = getIntersection3(v1, v2);
       //print(ret3);
   
       cout << "----------------三个有序数组的各个元素为" << endl;
       print(v1);
       print(v2);
       print(v3);
       vector<int> temp = getIntersection2(v1, v2);
       vector<int> ret4 = getIntersection2(temp, v3);
       print(ret4);
       return 0;
   }