#include<iostream>
using namespace std;

void merge(int* a, int* temp, int begin, int middle, int end){
	int i = begin;
	int j = middle + 1;
	int k = 0;
	while (i <= middle&&j <= end){//比較兩個指標所指向的元素，選擇相對小的元素放入到合併空間，並移動指標到下一位置
		if (a[i] < a[j])
			temp[k++] = a[i++];
		else
			temp[k++] = a[j++];
	}
	while (i <= middle)//若第一個序列有剩餘，直接拷貝出來粘到合併序列尾
		temp[k++] = a[i++];
	while (j <= end)//若第二個序列有剩餘，直接拷貝出來粘到合併序列尾
		temp[k++] = a[j++];
	for (i = 0; i < k; i++)//將排序好的序列拷貝回陣列中
		a[begin + i] = temp[i];
}
//遞迴版本
void merge_sort_recurse(int* a, int* temp, int begin, int end){
	int middle = (begin + end) >> 1;
	if (begin < end){
		merge_sort_recurse(a, temp, begin, middle);//左邊有序
		merge_sort_recurse(a, temp, middle + 1, end);//右邊有序
		merge(a, temp, begin, middle, end);//再將兩個有序數列合併
	}
}
//非遞迴版本，將a中相鄰長度為s的子序列兩兩歸併
void merge_pass(int* a, int* temp, int s, int len){
	int i = 0;
	int j;
	while (i < len - 2 * s + 1){
		merge(a, temp, i, i + s - 1, i + 2 * s - 1);
		i += 2 * s;
	}
	if (i < len - s + 1)//歸併最後兩個序列
		merge(a, temp, i, i + s - 1, len); 
}
void merge_sort_no_recurse(int* a, int len){
	int temp[1001];
	int k = 1;
	while (k <= len){
		merge_pass(a, temp, k, len);
		k *= 2; //子序列長度加倍
	}
}

int main(){
	int num1[1001] = { 50, 10, 90, 30, 70, 40, 80, 60, 20 };
	int temp1[1001];
	int num2[1001] = { 50, 10, 90, 30, 70, 40, 80, 60, 20 };
	int n = 9;

	merge_sort_recurse(num1, temp1, 0, n-1);
	for (int i = 0; i < n; i++)
		cout << num1[i] << " ";
	cout << endl;

	merge_sort_no_recurse(num2, n - 1);
	for (int i = 0; i < n; i++)
		cout << num2[i] << " ";
	cout << endl;
	
	return 0;
}