函数模板

[问题]

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。

[注意]
[1] 由于函数模板中使用了typename T::value_type，所以限制函数模板的实参不能为数组下标或者指针，只能使用容器的迭代器。
[2] 本文的函数模板方案适用于vector、list、deque等容器的迭代器。本题还可以用内存管理类allocator实现复制副本，但是此法将局限于只适用于vector迭代器。
#include <iostream>#include <vector>#include <string>#include <list>#include <deque>#include <algorithm>using std::string;using std::vector;using std::list;using std::deque;using std::cout;using std::endl;/* function template */template <typename T>typename T::value_type mostFre(T first, T last){// calculate the size of allocated memorystd::size_t amount=0;T start=first;while (start!=last){++amount;++start;}// aliastypedef std::vector<typename T::value_type> VecType;// create a duplicationVecType vec(amount);VecType::iterator newFirst=vec.begin();VecType::iterator newLast=vec.end();// copy input to duplication objectstd::uninitialized_copy(first,last,newFirst);// sort for duplicationstd::sort(newFirst,newLast);std::size_t maxOccu=0, occu=0;VecType::iterator preIter=newFirst;VecType::iterator maxOccuElemIt=newFirst;while (newFirst!=newLast){if (*newFirst!=*preIter){// checkif (occu>maxOccu){maxOccu=occu;maxOccuElemIt=preIter;// note, the previous one}occu=0;// reset}++occu;preIter=newFirst;++newFirst;}// do not forget the check "the last" elementif (occu>maxOccu){maxOccu=occu;maxOccuElemIt=preIter;// note, the previous one}return *maxOccuElemIt;}int main(){// test examplesint ia[]={1, 2, 3, 4, 5, 3, 3, 2, 2};double da[]={1.1, 2.2, 3.3, 4.4, 5.5, 3.3, 3.3, 2.2, 2.2};char ca[]={'a', 'b', 'c', 'd', 'e', 'c', 'c', 'b', 'b'};string sa[]={"wcdj", "is", "a", "guy", "wcdj", "is", "friendly", "to", "everyone"};vector<int> ivec(ia, ia+9);list<double> dlst(da, da+9);deque<char> cdqe(ca, ca+9);vector<string> svec(sa, sa+9);cout<<mostFre(ivec.begin(), ivec.end())<<endl;// 2cout<<mostFre(dlst.begin(), dlst.end())<<endl;// 2.2cout<<mostFre(cdqe.begin(), cdqe.end())<<endl;// bcout<<mostFre(svec.begin(), svec.end())<<endl;// isreturn 0;}