二路归并排序实现

来源：互联网发布：js拼接字符串的方法编辑：程序博客网时间：2024/06/07 23:48

一、归并算法思想

归并算法是建立在归并操作的基础上的。归并操作是指将两个或者多个以上的有序序列合并成一个新的序列，得到的新序列仍然有序。假设待排序序列大小为n，则初始状态下待排序序列有n个有序的子序列，其中每个子序列的大小为1，经过一次“两两归并”后，待排序序列将包含多个有序的大小为2的子序列。。。以此类推，直到整个序列有序。

算法演示

二、代码实现

#include <stdio.h>#include <stdlib.h>#include <time.h>#define DATA_SIZE10int*  init_data(int size);void print_data(int* pdata, int size);void swap(int* pdata, int i, int j);int  max(int* pdata, int i, int j);void do_sort(int *pdata, int size);void merge(int *pdata, int idx1, int len1, int idx2, int len2);void free_data(int *pdata);int main(){int *pdata = init_data(DATA_SIZE);if (NULL == pdata){return -1;}puts("Before sort:");print_data(pdata, DATA_SIZE);do_sort(pdata, DATA_SIZE);puts("After sort:");print_data(pdata, DATA_SIZE);free_data(pdata);return 0;}int*  init_data(int size){int *pdata = (int*)malloc(size*sizeof(int));if (NULL == pdata){return NULL;}int i;srand(time(NULL));for (i = 0 ; i < size ; ++i){pdata[i] = rand()%100;}return pdata;}void print_data(int* pdata, int size){int i;for (i = 0 ; i < size ; ++i){printf("%4d", pdata[i]);}printf("\n");}void swap(int* pdata, int i, int j){int tmp;tmp = pdata[i];pdata[i] = pdata[j];pdata[j] = tmp;}int  max(int* pdata, int i, int j){return pdata[i] >= pdata[j] ? i : j;}void do_sort(int *pdata, int size){int subseqlen = 1;int subseqnum = size;while (subseqlen < size){int mergetime = subseqnum / 2;int i;for (i = 0 ; i < mergetime ; ++i){int startidx1 = i*2*subseqlen;int len1 = subseqlen;int startidx2 = startidx1 + subseqlen;int len2 = (size -  startidx1 - len1) < subseqlen ? (size - startidx1 - len1) : subseqlen;merge(pdata, startidx1, len1, startidx2, len2);}subseqlen *= 2;subseqnum = (size + subseqlen - 1) / subseqlen;}}void merge(int *pdata, int startidx1, int len1, int startidx2, int len2){int *tmp;tmp = (int*)malloc((len1+len2)*sizeof(int));if (NULL ==  tmp){return;}int idx1 = startidx1;int idx2 = startidx2;int tmpidx = 0;while ((idx1 - startidx1) < len1 && (idx2 - startidx2) < len2){if (pdata[idx1] < pdata[idx2]){tmp[tmpidx] = pdata[idx1];idx1++;}else {tmp[tmpidx] = pdata[idx2];idx2++;}tmpidx++;}if ((idx1 - startidx1) < len1){while ((idx1 - startidx1) < len1){tmp[tmpidx] = pdata[idx1];idx1++;tmpidx++;}}else if ((idx2 - startidx2) < len2){ while ((idx2 - startidx2) < len2)        {tmp[tmpidx] = pdata[idx2];idx2++;tmpidx++;}}int j;for (j = 0; j < len1+len2 ; ++j){pdata[startidx1+j] = tmp[j];}free(tmp);}void free_data(int *pdata){free(pdata);pdata = NULL;}

0 0