算法導論——歸併排序

前面寫過選擇排序和插入排序，下面是歸併排序，如下：

#include<iostream>

using namespace std;
const int sentry = 999999;

void Merge( int ia[], size_t p, size_t q, size_t r)
{
	int a1[10], a2[10];
	size_t len1 = q - p + 1,len2=r-q;
	for (int i = 0; i <len1; ++i)
		a1[i] = ia[p+i];
	a1[len1] = sentry;
	for (int i = 0; i <len2; ++i)
		a2[i] = ia[q+i+1];
	a2[len2] = sentry;
	int b = 0, c = 0;
	for (int i = p; i <= r; ++i)
	{
		if (a1[b] >= a2[c])
			ia[i] = a2[c++];
		else
			ia[i] = a1[b++];
	}
}
void Merge_sort( int ia[],size_t p,size_t r)
{
	if (p < r )
	{
		int q = (p + r) / 2;
		Merge_sort(ia, p, q);
		Merge_sort(ia, q + 1, r);
		Merge(ia, p, q, r);
	}
}
int main()
{
	int a[20];
	int n;
	cout << "input the size of array:" << endl;
	cin >> n;
	for (int i = 0; i < n; ++i)
		cin >> a[i];								//input array
	Merge_sort(a, 0, n-1);
	for (int i = 0; i < n; ++i)
		cout << a[i] << " ";
	cout << endl;
	return 0;
}

寫了一下午終於完工。