分治之归并排序模版

/*
归并排序模版
对n个数进行排序
时间复杂度：O(nlogn);
利用分治思想，对比左半边和右边边放入一个暂时的数组进行排序
 */
#include <iostream>
using namespace std;
const int maxn = 1005;
int a[maxn], t[maxn];
void merge(int a[], int l, int m, int r)
{
    int i = l, j = m + 1, x = m, y = r, k = 0;
    while (i <= x && j <= y)
        if (a[i] < a[j]) t[k++] = a[i++];
        else t[k++] = a[j++];
    while (i <= x) t[k++] = a[i++];
    while (j <= y) t[k++] = a[j++];
    for (i = 0; i < k; ++i)
        a[l + i] = t[i];
}
void merge_sort(int a[], int l, int r)
{
    if (l >= r) return;
    int mid = (l + r) / 2;
    merge_sort(a, l, mid);
    merge_sort(a, mid + 1, r);
    merge(a, l, mid, r);
}
void print()
{
    for (int i = 0; i < 5; ++i)
        cout << a[i] << " ";
    cout << endl;
}
int main()
{
    for (int i = 0; i < 5; ++i)
        a[i] = 5 - i;
    print();
    merge_sort(a, 0, 4);
    print();
    return 0;
}