c - 使用多个排序条件对数组进行排序(快速排序)

Question

我正在尝试找出如何(使用快速排序算法)按 2 个标准对结构数组进行排序。例如说我有一个结构:

struct employee{
   char gender[12];
   char name[12];
   int id;
};

假设我的输入是:

struct employee arr[3]=
{
    {"male","Matt",1234},
    {"female","Jessica",2345},
    {"male","Josh",1235}
};

我想先按性别对元素进行排序，然后按升序对 ID 进行排序。一个例子是让所有男性首先按顺序打印他们的 ID，然后是所有女性。我试图在不使用 qsort 函数的情况下执行此操作，但我一点也不知道如何检查 .这是我的排序功能:

void quicksort(struct employee *arr, int left, int right)
{
    int pivot, l, r, temp;
    if(left < right)
    {
        p = left;
        l = left;
        r = right;
        while(l < r)
        {

            while(arr[l].id <= arr[p].id && l <= right)
                l++;
            while(arr[r].id > arr[p].id && r >= left)
                r--;

            if(l < r)
            {
                temp = arr[l].id;
                arr[l].id = arr[r].id;
                arr[r].id = temp;
            }
        }


        temp = arr[r].id;
        arr[r].id = arr[p].id;
        arr[p].id = temp;

        quicksort(arr, left, r-1);
        quicksort(arr, r+1, right);
    }
}

有什么建议吗？我在想我可以使用 strcmp 但我无法弄清楚将它包含在函数中的什么地方。

Answer 1

您当然可以内联比较函数，以及与此相关的交换器。下面的这段代码非常基础，依赖于有效的指针，但你明白了。我还冒昧地削减了您的快速排序，修复了过程中出现的问题(我希望如此)。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// employee record
struct employee
{
    char gender[12];
    char name[12];
    int id;
};

// swap employee records
void swap_employee(struct employee *left, struct employee *right)
{
    struct employee tmp = *right;
    *right = *left;
    *left = tmp;
}

// compare employee records
int compare_employee(const struct employee* left,
                     const struct employee* right)
{
    int gender = strcmp(left->gender, right->gender);
    return (gender ? gender : (left->id - right->id));
}

// quicksort for employees
static void quicksort_(struct employee *arr, int left, int right)
{
    struct employee p = arr[(left+right)/2];    // as good as any
    int l = left, r = right;   // movable indicies

    while (l <= r)
    {
        while (compare_employee(arr+l, &p) < 0)
            ++l;
        while (compare_employee(arr+r, &p) > 0)
            --r;
        if (l <= r)
        {
            swap_employee(arr+l, arr+r);
            ++l; --r;
        }
    }

    if (left < r)
        quicksort_(arr, left, r);
    if (l < right)
        quicksort_(arr, l, right);
}

// exposed API
void quicksort(struct employee *arr, int count)
{
    if (arr && (count>0))
        quicksort_(arr, 0, count-1);
}

/* sample usage */
int main(int argc, char *argv[])
{
    struct employee arr[]=
    {
        {"male","Matt",1234},
        {"female","Jessica",2345},
        {"male","Josh",1235},
        {"female","Betsy",2344},
        {"male","Roger",1233}
    };

    quicksort(arr, sizeof(arr)/sizeof(arr[0]));

    for (int i=0;i<sizeof(arr)/sizeof(arr[0]);++i)
        printf("%s, %s, %d\n", arr[i].gender,arr[i].name, arr[i].id);

    return EXIT_SUCCESS;
}

结果

female, Betsy, 2344
female, Jessica, 2345
male, Roger, 1233
male, Matt, 1234
male, Josh, 1235