136 lines
3.8 KiB
C++
136 lines
3.8 KiB
C++
#include "stdio.h" /*
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链表的归并排序的核心是将链表分成前后两段，分别排序后对两个有序链表归并，递归边界是当前链表长度为1。
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！！！注意：此代码为可运行版本，目的是让大家检验自己的实验结果是否正确
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！！！其中的链表节点是通过结构体实现的，实际汇编的实现中指针也是32位整数，请参考另一个版本的代码（merge_sort.cpp）
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*/
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// 统计待排序数据的比较次数
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int compare_count = 0;
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// 链表节点, 结构体实现
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struct Node
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{
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int value;
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Node *next;
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};
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// 两个有序链表合并，将右链元素插入到左链中 。
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Node *merge(Node *l_head, Node *r_head)
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{
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// 这里构建一个虚拟头结点，方便在第一个元素前插入。
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Node *head = new Node;
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head->next = l_head;
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Node *p_left = head;
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Node *p_right = r_head;
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do
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{
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do
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{ // 寻找左链中的插入位置
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if (p_left->next == (int)NULL)
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break;
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compare_count++; // 统计比较次数
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if ((p_left->next)->value > p_right->value)
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break;
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p_left = p_left->next;
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} while (1);
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// 如果到达左链尾端，右链直接接上
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if (p_left->next == NULL)
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{
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p_left->next = p_right;
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break;
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}
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Node *p_right_temp = p_right;
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do
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{ // 寻找右链待插入片段
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if (p_right_temp->next == NULL)
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break;
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compare_count++; // 统计比较次数
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if ((p_right_temp->next)->value > (p_left->next)->value)
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break;
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p_right_temp = p_right_temp->next;
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} while (1);
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// 完成插入操作
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Node *temp_right_pointer_next = p_right_temp->next;
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p_right_temp->next = p_left->next;
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p_left->next = p_right;
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p_left = p_right_temp;
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p_right = temp_right_pointer_next;
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if (p_right == NULL)
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break;
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} while (1);
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Node *rv = head->next;
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delete head;
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return rv;
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}
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// 归并排序主函数，先找链表中点，再分别排序，最后归并
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Node *msort(Node *head)
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{
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if (head->next == NULL)
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return head;
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Node *stride_2_pointer = head;
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Node *stride_1_pointer = head;
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do
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{ // 通过同时进行步长为 1 和步长为 2 的跳转找中点
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if (stride_2_pointer->next == NULL)
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break;
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stride_2_pointer = stride_2_pointer->next;
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if (stride_2_pointer->next == NULL)
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break;
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stride_2_pointer = stride_2_pointer->next;
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stride_1_pointer = stride_1_pointer->next;
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} while (1);
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// 拆成两个链表分别排序 ， 再归并 。
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stride_2_pointer = stride_1_pointer->next;
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stride_1_pointer->next = NULL;
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Node *l_head = msort(head);
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Node *r_head = msort(stride_2_pointer);
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return merge(l_head, r_head);
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}
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int main()
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{
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FILE *infile, *outfile;
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int buffer[1001];
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infile = fopen("a.in", "rb");
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fread(buffer, 4, 1001, infile);
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fclose(infile);
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int N = buffer[0];
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Node *head = new Node;
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head->next = NULL;
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Node *pointer = head;
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for (int idx = 1; idx <= N; idx++)
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{
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pointer->next = new Node;
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pointer = pointer->next;
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pointer->value = buffer[idx];
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pointer->next = NULL;
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}
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// 排序
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head->next = msort(head->next);
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// 输出到文件
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pointer = head;
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outfile = fopen("a.out", "wb");
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// 输出比较次数
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fwrite(&compare_count, 4, 1, outfile);
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do
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{
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pointer = pointer->next;
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if (pointer == NULL)
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break;
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fwrite(&(pointer->value), 4, 1, outfile);
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} while (1);
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fclose(outfile);
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// 释放链表内存
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while (head != NULL)
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{
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Node *temp = head;
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head = head->next;
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delete temp;
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}
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return 0;
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}
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