写了一个类似STL中的sort用法的归并排序，可以以函数形式传入排序规则。

#include <algorithm>
#include <iostream>
#include <vector>
#include <functional>

using namespace std;

template <typename T>
class MergeSort{
public:
    //以仿函数实现
    void operator()(vector<T>& data, function<bool(T, T)> func) {
        this->func =func;
        MSort(data, 0, data.size() - 1);
    }
private:
    //排序规则
    function<bool(T, T)> func;
    //归并排序
    void MSort(vector<T>& data, int low, int high){
        if(low >= high){
            return;
        }
        int mid = (low+high)/2;
        MSort(data, low, mid);
        MSort(data, mid + 1, high);
        Merge(data,low, mid, high);
    }
    //归并
    void Merge(vector<T> &list1, const int low,const  int mid, const int high){
        vector<T> temp;
        //预先分配100空间，提高vector效率
        temp.reserve(100);
        int low_iter = low;
        int high_iter = mid + 1;

        while (low_iter <= mid && high_iter <= high){
            //以传入的判断函数进行比较
            if(func(list1[low_iter] , list1[high_iter])){
                temp.push_back(list1[low_iter++]);
            }else{
                temp.push_back(list1[high_iter++]);
            }
        }
        if(low_iter > mid && high_iter <= high){
            for(int i = high_iter; i <= high; i++)
                temp.push_back(list1[i]);
        }
        else if(low_iter <= mid && high_iter > high){
            for(int i = low_iter; i <= mid; i++){
                temp.push_back(list1[i]);
            }
        }
        for(int i = low, j = 0; i <= high; i++, j++){
            list1[i] = temp[j];
        }
    }
};

int main(){
    vector<int> a1 = {1,3,5,2,4,6,99,1,2,3};
    //以lambda表达式形式传入比较函数，返回值为boolen类型
    MergeSort<int>()(a1, [](int a, int b){ return a <= b;});
    for_each(a1.begin(), a1.end(), [](int i){cout << i << " ";});
}