归并排序

终于能独立写出归并排序了， 虽然这是递归版的， 但非递归版的也即将出炉

具体思路:

归并排序其实要做两件事：

（1）“分解”——将序列每次折半划分。

（2）“合并”——将划分后的序列段两两合并后排序。

#include <iostream>

#include <cstdio>
#include <cstdlib>
#include <ctime>
const int maxn = 1e3;
using namespace std;
/*合并*/
void Merge (int a[], int low, int mid, int high) {
    int L[maxn], R[maxn];
    for (int i = low; i <= mid; i++)
        L[i] = a[i];
    for (int j = mid + 1; j <= high; j++)
        R[j] = a[j];
    int i = low;
    int j = mid + 1;
    R[high + 1] = L[mid + 1] = 0x3f3f3f3f;  //设置哨兵
    for (int k = low; k <= high; k++)
        if (L[i] <= R[j])
            a[k] = L[i++];
        else
            a[k] = R[j++];
}
/*分*/
void MergeSort (int a[], int low, int mid, int high) {
    if (low < high) {
        MergeSort(a, low, (low + mid) / 2, mid);
        MergeSort(a, mid + 1, (mid + 1 + high) / 2, high);
        Merge(a, low, mid, high);
    }
}
int main()
{
    int a[maxn];
    int n;
    printf("请问要生成几个随机数:");
    cin >> n;
    printf("生成的%d个数:", n);
    srand((unsigned)time(NULL));
    for (int i = 0; i < n; i++) {
        a[i] = rand() % 100;
        if (i == 0)
            cout << a[i] << endl;
        else
            cout << " " << a[i];
    }
    cout << endl;
    int low = 0;
    int high = n - 1;
    int mid = (n - 1) / 2;
    MergeSort(a, low, mid, high);
    for (int i = 0; i < n; i++)
        if (i == 0)
            cout << a[i];
        else
            cout << " " << a[i];
    cout << endl;
    return 0;
}