C++ 模板编程 初级问题

不知道错在哪里
要求如下
Exercise
16.12:
Write a function template that takes a pair of values that represent iterators of unknown type.
Find the value that occurs most frequently in the sequence.
编写一个函数模板，接受表示未知类型迭代器的一对值，找出在序列中出现得最频繁的值。

#include <iostream>
#include <vector>
#include <map>

using namespace std;


template<typename T, typename CT>
void countfrenquency(T &first, T &last)
{
    map<CT, int> ctmap;
    typename map<CT, int>::iterator ctiit;
    int sum = 0;
    CT max;
    for (T t = first; t != last; t++)
    {
        if (!ctmap.find(*t))
        {
            ctmap.insert(*t);
        }
        else
        {
            ctmap[*t]++;
        }
    }
    ctiit = ctmap.begin();
    while (ctiit != ctmap.end())
    {
        if ((*ctiit) > sum)
        {
            sum = ctmap[*ctiit];
            max = *ctiit;
        }
    }
    cout << max << endl;
}


int main()
{
    std::cout << "Hello World!\n";

    vector<int> iv({ 1,1,2,3,4,6 });
    typedef vector<int>::iterator ivit;
    countfrenquency<ivit &, int &>(iv.begin(), iv.end());
}

报错提示：

求解！

给你一个新代码！望采纳！

#include <iostream> 
#include <vector> 
#include <string> 
#include <algorithm> 


using namespace std; 


template <typename T> 
typename T mosFre(T first,T last) 
{  
sort(first,last); 
size_t maxOccu = 0,occu = 0; 
T preIter = first,maxOccuElemIt = first; 


while(first != last) 
{ 
if(*first != *preIter) 
{ 
if(occu >maxOccu) 
{ 
maxOccu = occu; 
maxOccuElemIt = preIter; 
} 
occu = 0; 
} 
++occu; 
preIter = first; 
++first; 
} 


//occur count of the last value compare to the current maxcount 


if(occu > maxOccu) 
{ 
maxOccu = occu; 
maxOccuElemIt = preIter; 
} 
return maxOccuElemIt; 
} 


int main() 
{ 
int ia[] = {2,2,3,3,3,6}; 
vector <int> ivec(ia,ia+sizeof(ia)/sizeof(int)); 
cout <<*mosFre(ivec.begin(),ivec.end())<<endl; 
system("pause"); 
    return 0; 
}