122 lines
3.5 KiB
C++
122 lines
3.5 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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*/
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int compare_count = 0;
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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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int *merge(int *l_head, int *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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int *head = new int[2];
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head[1] = (int)l_head;
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int *p_left = head;
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int *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[1] == (int)NULL)
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break;
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// count the number of comparisons
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compare_count++;
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if (((int *)p_left[1])[0] > p_right[0])
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break;
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p_left = (int *)p_left[1];
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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[1] == (int)NULL)
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{
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p_left[1] = (int)p_right;
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break;
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}
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int *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[1] == (int)NULL)
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break;
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// count the number of comparisons
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compare_count++;
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if (((int *)p_right_temp[1])[0] > ((int *)p_left[1])[0])
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break;
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p_right_temp = (int *)p_right_temp[1];
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} while (1);
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// 完成插入操作
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int *temp_right_pointer_next = (int *)p_right_temp[1];
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p_right_temp[1] = p_left[1];
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p_left[1] = (int)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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int rv = head[1];
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delete head;
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return (int *)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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int *msort(int *head)
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{
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if (head[1] == (int)NULL)
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return head;
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int *stride_2_pointer = head;
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int *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[1] == (int)NULL)
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break;
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stride_2_pointer = (int *)stride_2_pointer[1];
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if (stride_2_pointer[1] == (int)NULL)
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break;
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stride_2_pointer = (int *)stride_2_pointer[1];
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stride_1_pointer = (int *)stride_1_pointer[1];
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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 = (int *)stride_1_pointer[1];
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stride_1_pointer[1] = (int)NULL;
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int *l_head = msort(head);
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int *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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// create a linked list
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int *head = new int[2];
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head[1] = (int)NULL;
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int *pointer = head;
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for (int idx = 1; idx <= N; idx++)
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{
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pointer[1] = (int)new int[2];
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pointer = (int *)pointer[1];
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pointer[0] = buffer[idx];
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pointer[1] = (int)NULL;
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}
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// sort
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head[1] = (int)msort((int *)head[1]);
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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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// wirte the sorted list to file
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do
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{
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pointer = (int *)pointer[1];
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if (pointer == NULL)
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break;
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fwrite(pointer, 4, 1, outfile);
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} while (1);
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fclose(outfile);
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// 本文件用于翻译，没有释放链表内存的操作
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return 0;
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}
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