排序算法

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这周没时间做算法作业，不过自己在上学期做了选择排序，归并排序，以及快速排序，这个快速排序是原地排序，比一般的快速排序更快，这里贴上代码，未做的作业会过几天补上的，上学期我在实现这个算法的时候是采用随机生成200W数据进行时间测试的，测试结果如下：

快速排序：4.1s

归并排序：6.1s

快速排序：

#include <stdio.h>#include <stdlib.h>#define LEN 20000000 int a[LEN];//int a[LEN] = {7, 4, 6, 4, 2, 4, 1, 8};void initialize(void){int i;for (i = 0; i < LEN; i++)a[i] = rand();}void print(void){int i;for (i = 0; i < LEN; i++)printf("%d ", a[i]);printf("\n");}void swap(int *a, int *b){int tmp;tmp = *a;*a = *b;*b = tmp;}int partition(int start, int end){int i = start + 1;int j = end;int key = a[start];while (1) {while (a[i] <= key && i < j) i++;while (a[j] > key && j > i) j--;if (i == j) {if (a[i] <= key) {swap(&a[start], &a[i]);return i;} else {swap(&a[start], &a[--i]);return i;}}swap(&a[i], &a[j]);}}void quick_sort(int start, int end){if (start < end) {int mid = partition(start, end);quick_sort(start, mid - 1);quick_sort(mid+1, end);}}int main(void){initialize();quick_sort(0, LEN - 1);//print();return 0;

归并排序：

#include<stdio.h>#include <stdlib.h>#define LEN 2000000//int a[LEN] = {5, 2, 4, 7, 1, 3, 2, 6};int a[LEN];void initialize(void){int i;for (i = 0; i < LEN; i++)a[i] = rand();}void merge(int start, int mid, int end){int l = mid - start + 1;int r = end - mid;int left[l];int right[r];int i, j, k;for (i = 0; i < l; i++)left[i] = a[start + i];for (i = 0; i < r; i++)right[i] = a[mid + 1 + i]; j = k = 0;i = start;while (j < l || k < r) {if (left[j] < right[k]) {if (j < l)a[i++] = left[j++];elsea[i++] = right[k++];} else {if (k < r)a[i++] = right[k++];elsea[i++] = left[j++];}}}void sort(int start, int end){int mid = (start + end) / 2;if (start < end) {sort(start, mid);sort(mid + 1, end);merge(start, mid, end);}}void print(void){int i;for (i = 0; i < LEN; i++)printf("%d ", a[i]);printf("\n");}int main(void){initialize();sort(0, LEN - 1);//print();return 0;}

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