算法之路——归并排序

　　归并排序是令一类排序方法。即：将多个有序的表合成一个新的有序的表。这里主要是2—路归并排序。

　　可以用递归和非递归的方法实现。

实现代码如下：

/*这是merge_sort.h文件*/
#ifndef merge_sort
    #define merge_sort

#define MAXSIZE 100
typedef int KeyType;

typedef struct {
    KeyType    data;
    //其他的属性
}RedType,* PRedType;

typedef struct {
    RedType list[MAXSIZE];
    int length;
}SqList, * PSqList;

#define K_T "%d"            //用于输入输出 如 printf(K_T, p->list[i].data);

#define OK    0
#define P_NULL    1
#define TOOBIG    2
#define NUM_ERROR    3

int inputList (PSqList p,int length);
int outputList (PSqList p);
int mergeSort (PSqList p, PSqList d, int (*comp)(void *, void *));
#endif

/*这是merge_sort.cpp文件*/
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include "merge_sort.h"

int inputList (PSqList p,int length) 
{//输入序列
    
    if (p == NULL)
        return P_NULL;        //1，指针是空的
    if (length > MAXSIZE)
        return TOOBIG;         //2，要输入的序列太多
srand(time(NULL));
    int i = 0;
    for (i = 0; i < length; i++)
        p->list[i].data = rand()%10000;
        //if (scanf(K_T,&(p->list[i].data)) != 1)
        //    return NUM_ERROR;  //3，输入的数字有误
    p->length = length;
    return OK;    //0
}

int outputList (PSqList p) 
{//输出序列
    if (p == NULL)
        return P_NULL;
    
    int i = 0;
    for (i =0; i < p->length; i++) 
        printf (K_T"\t",p->list[i].data);
    putchar('\n');
    return OK;
}//outputList

static int merge (PSqList p, PSqList d,int (*comp)(void *,void *), int s, int m, int n)
{
    //本来是没使用tmp作为中转的，后来考虑到，如果p和d是一个列表就会出现问题。而且下面给的非递归版的归并排序，p和d是同以个列表
    PSqList tmp;        //如果用全局变量就不用每次申请了
    tmp = (PSqList)malloc(sizeof(SqList));
    tmp->length = p->length;
    int i = s;
    int j = m + 1;
    int k = s;

    while (i <= m && j <= n)
    {
        if (comp(&(p->list[i]), &(p->list[j])) < 0)
            tmp->list[k++] = p->list[i++];
        else
            tmp->list[k++] = p->list[j++];
    }

    while (i <= m)
        tmp->list[k++] = p->list[i++];

    while (j <= n)
        tmp->list[k++] = p->list[j++];

    for (i = s; i <= n; i++)
        d->list[i] = tmp->list[i];
    free(tmp);
    return 0;
}

static int mSort (PSqList p, PSqList d, int (*comp)(void *, void *), int s, int n)
{
    if (s == n)
    {
        d->list[s] = p->list[s];
        return 0;
    }
    SqList t;
    t.length = p->length;

    int m;
    m = (s + n)/2;

    mSort(p, &t, comp, s, m);
    mSort(p, &t, comp, m + 1, n);
    merge(&t, d, comp, s, m, n);
    return OK;
}//mSort


int mergeSort (PSqList p, PSqList d, int (*comp)(void *, void *))
{
    mSort (p, d, comp, 0, p->length-1);
    return OK;
}

/*
int mergeSort (PSqList p, PSqList d,int (*comp)(void *, void *))
{//这是非递归实现的归并排序，第二个参数是不需要的，这里只是为了和之前的函数兼容
//将p归并排序，需要改变原本的p列表的内容，排序后的结果还是保留在p中。如果要不改变p并且将排序后的结果放在d中则只需开辟一个中转站即可
    d = p;
    int i,j;
    for (i = 1; i < p->length; i*=2)
    {
        for (j = 0; j+2*i-1 < p->length; j = j+2*i)
        {
            merge (p, d, comp, j, j+i-1, j+2*i-1);
        }
        if (j+i-1 <p->length-1)
            merge (p, d, comp, j, j+i-1, p->length-1);
    }
    return OK;
}
*/

/*这是main.cpp文件*/
#include <stdio.h>
#include <stdlib.h>
#include "merge_sort.h"
int comp(void *, void *);
int main (int argc, char * argv) 
{
    int status;
    PSqList test;
    test = (PSqList)malloc(sizeof(SqList));
    PSqList dist;
    dist = (PSqList)malloc(sizeof(SqList));
    int n = 0 ;
    printf("请输入第一组待排序的数的个数(输入0结束循环)：");
    
    while (1)
    {
        while (scanf("%d",&n) != 1)
        {
            puts("输入有误！请重新输入！");
            while(getchar() != '\n');    
        }

        if (n == 0)                //结束
            break;
        if (status = inputList(test, n) != 0)
        {
            puts("输入的数字有误！");
            while(getchar() != '\n');
            //exit(status);
        }

        dist->length = n;
        mergeSort(test, dist, comp);
        outputList (dist);
        printf("请输入下一组待排序的数的个数(输入0结束循环)：");
    }
    free(test);
    free(dist);
    return 0;
}

int comp(void * d1, void * d2)
{//比较函数
    return (((PRedType)d1)->data - ((PRedType)d2)->data );
}