二路归并排序的C++实现

#include<iostream>
#include<vector>
using namespace std;

typedef int elem;

void mergeArray(vector<elem>&, int, int, int, int (*)(elem, elem));
void mergeSort(vector<elem>&, int, int, int (*)(elem, elem));
int comp(elem, elem);

int main(void){
    
    
	elem a[]{
    
    4, 6, 5, 1, 7, 2};
	vector<elem> v(a, a+6);
	
	mergeSort(v, 0, 5, comp); 
	
	for (vector<elem>::iterator it=v.begin(); it!=v.end(); ++it)
		cout<<*it<<" ";
		
	return 0;
}

int comp(elem a, elem b){
    
     
	return a-b; //升序 
	//return b-a; //降序
}

void mergeArray(vector<elem>& v, int start, int mid, int end, int (*cmp)(elem, elem)){
    
    
	if(start >= end)
		return;	
	int i=start, j=mid+1;
	vector<elem> temp;
		
	while (i<=mid && j<=end){
    
    
		if(cmp(v[i], v[j]) <= 0){
    
    
			temp.push_back(v[i++]);
		}
		else{
    
    
			temp.push_back(v[j++]);
		}
	}	
	while (i<=mid){
    
    
		temp.push_back(v[i++]);
	}
	while (j<=end){
    
    
		temp.push_back(v[j++]);
	}
	for (int i=start; i<=end;++i)
		v[i] = temp[i-start];
}

void mergeSort(vector<elem>& v, int start, int end, int (*cmp)(elem, elem)){
    
    
	if(start >= end)
		return;
	int mid = (start + end) / 2;	
	mergeSort(v, start, mid, cmp);
	mergeSort(v, mid+1, end, cmp);
	mergeArray(v, start, mid, end, cmp);	
}