Mergesort——归并排序

#include <iostream>
#include <cstdio>
using namespace std;
int count = 0;
void merge(int a[], int first, int mid, int last, int temp[])
{
	int i = first, j = mid+1, k = 0;
	while(i <= mid&&j <= last)
	{
		if(a[i] > a[j])
		{
			temp[k++] = a[j++];
			count += mid-i+1;
		}	
		else
			temp[k++] = a[i++];
	}
	while(i <= mid)
		temp[k++] = a[i++];
	while(j <= last)
		temp[k++] = a[j++];
	for(i = 0; i < k; i++)
	{
		a[first+i] = temp[i];
	}
}
void mergesort(int source[], int temp[], int first, int last)
{
	int mid = (first + last)/2;
	if(first < last)
	{
		mergesort(source, temp, first, mid);
		mergesort(source, temp, mid+1, last);
		merge(source, first, mid, last, temp);
	}
	
}
int main()
{
	int n;
	int a[100], b[100];
	cin >> n;
	for(int i = 0; i < n; i++)
	{
		cin >> a[i];
	}
	mergesort(a, b, 0, n-1);
	for(int i = 0; i < n; i++)
	{
		cout << a[i] << " ";
	}
	cout << endl;
	cout << count;
}