大神的世界

這裡我們實做兩種交換方式

1. 將陣列宣告在 stack，交換時必須搬移多個元素

2. 用指標指向陣列，交換時只改變指標指向的位址

#include <algorithm>
#include <iostream>
#include <ctime>

using namespace std;

int cmp1(const void *_a, const void *_b)
{
    const int *a = (const int *)_a,
              *b = (const int *)_b;

    return a[1] > b[1];
}

int cmp2(const void *_a, const void *_b)
{
    const int *a = *(const int * const *)_a,
              *b = *(const int * const *)_b;

    return a[1] > b[1];
}

int main()
{
    clock_t start, end;
    constexpr int len = 10000;

    int arr1[10][len];

    for(int i = 0; i<10; i+=1)
        for(int j = 0; j<len; j+=1)
            arr1[i][j] = len-j;
    

    start = clock();
    qsort(arr1, 10, sizeof(arr1[0]), cmp1);
    end = clock();

    cout << "time: " << end - start << endl;

    int **arr2 = new int*[10];
    for(int i = 0; i<10; i+=1){
        arr2[i] = new int[len];
        for(int j = 0; j<len; j+=1)
            arr2[i][j] = len-j;
    }

    start = clock();
    qsort(arr2, 10, sizeof(arr2[0]), cmp2);
    end = clock();
    cout << "time: " << end - start << endl;
}