七大排序之归并排序

#include<iostream>
#include<time.h>
#include<stdlib.h>
#include<sys/timeb.h>
using namespace std;

const int Max = 9999;

void swap(int& a, int& b) {
    int temp = a;
    a = b;
    b = temp;
}


long getSystemTime() {
    struct timeb tb;
    ftime(&tb);
    return tb.time * 1000 + tb.millitm;
}
void Print(const int* arr, int length) {
    for (int i = 0; i < length; i++) {
        cout << arr[i] << " ";
    }

}
void Merge(int* arr,int start,int end,int mid,int* temp) {
    int i_start = start;
    int i_end = mid;
    int j_start = mid + 1;
    int j_end = end;
    int length = 0;
    while (i_start <= i_end && j_start <= j_end) {
        if (arr[i_start] < arr[j_start]) {
            temp[length] = arr[i_start];
            length++;
            i_start++;
        }
        else
        {
            temp[length] = arr[j_start];
            length++;
            j_start++;
        }
    }
    while (i_start<=i_end)
    {
        temp[length] = arr[i_start];
        length++;
        i_start++;
    }
    while (j_start <= j_end)
    {
        temp[length] = arr[j_start];
        length++;
        j_start++;
    }
    for (int i = 0; i < length; i++) {
        arr[start+i] = temp[i];//注意是不是arr[i]
    }
}
void MergeSort(int* arr, int start, int end, int* temp) {
    if (start == end) return;
    int mid = (start + end) / 2;
    MergeSort(arr, start, mid,temp);
    MergeSort(arr, mid + 1, end, temp);

    Merge(arr, start, end, mid, temp);
}

int main() {
    int arr[Max];
    int tmp[Max];
    srand((unsigned)time(NULL));
    for (int i = 0; i < Max; i++) {
        arr[i] = rand() % Max;
    }
    //cout << "排序前：\n";
    //Print(arr, Max);
    long pt = getSystemTime();
    MergeSort(arr,0,Max-1,tmp);
    long at = getSystemTime();
    //cout << "\n排序后：\n";
    //Print(arr, Max);

    cout << "\ntime of sort:" << at - pt << "ms\n";


    return 0;
}