「算法导论」：归并排序

时间复杂度：o(nlgn)

空间复杂度：s(n)

代码：

/*************************************************************************
	> File Name: merge_sort.cpp
	> Author sangoly
	> Mail: sangoly@aliyun.com 
	> Created Time: 2014年06月30日 星期一 20时32分44秒
 ************************************************************************/

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

void merge(int list[], int start, int middle, int end) {
	int llen = middle - start + 1;
	int rlen = end - middle;

	int* larr = new int[llen + 1];
	int* rarr = new int[rlen + 1];

	int i, j;
	for (i = 0; i < llen; i++) {
		larr[i] = list[start + i];
	}
	for (j = 0; j < rlen; j++) {
		rarr[j] = list[middle + 1 + j];
	}
	// Add the guard
	larr[llen] = numeric_limits<int>::max();
	rarr[rlen] = numeric_limits<int>::max();

	i = j = 0;
	for (int k = start; k <= end; k++) {
		if (larr[i] <= rarr[j])
			list[k] = larr[i++];
		else
			list[k] = rarr[j++];
	}
	delete [] larr;
	delete [] rarr;
}

void merge_sort(int list[], int start, int end) {
	if (start >= end)
		return;
	int middle = (start + end) / 2;
	merge_sort(list, start, middle);
	merge_sort(list, middle + 1, end);
	merge(list, start, middle, end);
}

int main() {
	int list[8] = {5, 10, 4, 7, 1, 15, 2, 6};
	merge_sort(list, 0, 7);
	for (int i = 0; i < 8; i++)
		cout<<list[i]<<" ";
	cout<<endl;
	return 0;
}