算法导论代码 第2章 算法入门

前言

这文档是根据《算法导论》第2版的伪代码用C语言写的代码，因为用到了c99的一些特性，如变长数组。需要用gcc指定选项-std=c99编译，不支持VC。

参考书：

算法导论第2版电子版:

http://www.kuaipan.cn/file/id_12008874588516081.html

C语言程序设计_现代方法(第2版)电子版:

http://www.kuaipan.cn/file/id_12008874588516159.html

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　By 小鹏，QQ:562453464

　　　　　　　　　                            2011.11.30

第2章 算法入门

2.1 插入排序

#include <stdio.h>#include <string.h>#include <time.h>#include <stdlib.h>void insertion_sort(void *base, size_t elem_size, size_t n,    int (*comp) (const void *, const void *)){char *cbase = base;char key[elem_size];for (size_t i = 1; i < n; i++) {memcpy(key, &cbase[i * elem_size], elem_size);/*把base[i]插入到排好序的base[0..i-1]中 */int j = i - 1;while (j >= 0 && comp(&cbase[j * elem_size], key) > 0) {memcpy(&cbase[(j + 1) * elem_size],       &cbase[j * elem_size], elem_size);j--;}memcpy(&cbase[(j + 1) * elem_size], key, elem_size);}}void swap(void *a, void *b, size_t elem_size){if(a==NULL||b==NULL||a==b)return;char temp[elem_size];/*变长数组 */memcpy(temp, a, elem_size);memcpy(a, b, elem_size);memcpy(b, temp, elem_size);}void randomized_in_place(void *array, size_t elem_size, int n){char *carray = array;for (int i = 0; i < n; i++) {int index = rand() % (n - i) + i;swap(&carray[i * elem_size], &carray[index * elem_size],     elem_size);}}void print_array(int a[], int n){for (int i = 0; i < n; i++) {printf("%d ", a[i]);}printf("\n");}int cmp_int(const void *p1, const void *p2){const int *pa = p1;const int *pb = p2;if (*pa < *pb)return -1;if (*pa == *pb)return 0;return 1;}int main(void){srand((unsigned)time(NULL));int a[10];for (int i = 0; i < 10; i++) {a[i] = i;}randomized_in_place(a, sizeof(int), 10);printf("排序前:\n");print_array(a, 10);insertion_sort(a, sizeof(int), 10, cmp_int);printf("排序后:\n");print_array(a, 10);return 0;}

2.3 归并排序

#include <stdio.h>#include <limits.h>#include <stdlib.h>#include <string.h>#include <time.h>void merge(void *base, size_t elem_size, size_t left, size_t middle,   size_t right, void *max, int (*comp) (const void *, const void *),   void *buff){char *cbase = base;char *cbuff = buff;size_t left_length = middle - left + 1;size_t right_length = right - middle;char *left_buff = cbuff;char *right_buff = &cbuff[(left_length + 1) * elem_size];for (size_t i = 0; i < left_length; i++) {memcpy(&left_buff[i * elem_size],       &cbase[(left + i) * elem_size], elem_size);}memcpy(&left_buff[left_length * elem_size], max, elem_size);for (size_t i = 0; i < right_length; i++) {memcpy(&right_buff[i * elem_size],       &cbase[(middle + 1 + i) * elem_size], elem_size);}memcpy(&right_buff[right_length * elem_size], max, elem_size);for (size_t k = left, i = 0, j = 0; k <= right; k++) {if (comp(&left_buff[i * elem_size], &right_buff[j * elem_size])    <= 0) {memcpy(&cbase[k * elem_size], &left_buff[i * elem_size],       elem_size);i++;} else {memcpy(&cbase[k * elem_size],       &right_buff[j * elem_size], elem_size);j++;}}}void merge_sort_buff(void *base, size_t elem_size, size_t left, size_t right,     void *max, int (*comp) (const void *, const void *),     void *buff){if (left < right) {size_t middle = (left + right) / 2;merge_sort_buff(base, elem_size, left, middle, max, comp, buff);merge_sort_buff(base, elem_size, middle + 1, right, max, comp,buff);merge(base, elem_size, left, middle, right, max, comp, buff);}}void merge_sort(void *base, size_t elem_size, size_t left, size_t right,void *max, int (*comp) (const void *, const void *)){if (left >= right)return;size_t length = right - left + 1;/*数组的长度 */char buff[(length + 2) * elem_size];/*+2是因为要在缓存保存两个最大值 */merge_sort_buff(base, elem_size, left, right, max, comp, buff);}void swap(void *a, void *b, size_t elem_size){if(a==NULL||b==NULL||a==b)return;char temp[elem_size];/*变长数组 */memcpy(temp, a, elem_size);memcpy(a, b, elem_size);memcpy(b, temp, elem_size);}void randomized_in_place(void *array, size_t elem_size, int n){char *c_array = array;for (int i = 0; i < n; i++) {int index = rand() % (n - i) + i;swap(&c_array[i * elem_size], &c_array[index * elem_size],     elem_size);}}void print_array(int a[], int n){for (int i = 0; i < n; i++) {printf("%d ", a[i]);}printf("\n");}int cmp_int(const void *p1, const void *p2){const int *pa = p1;const int *pb = p2;if (*pa < *pb)return -1;if (*pa == *pb)return 0;return 1;}int main(void){srand((unsigned)time(NULL));int a[10];for (int i = 0; i < 10; i++) {a[i] = i;}randomized_in_place(a, sizeof(int), 10);printf("排序前:\n");print_array(a, 10);int max_int = INT_MAX;merge_sort(a, sizeof(int), 0, 9, &max_int, cmp_int);printf("排序后:\n");print_array(a, 10);return 0;}