冒泡排序运行的时间和归并排序运行时间的比较

下面是一万个随机数据采用冒泡排序所用的时间（由于老师给的一百万个数据太大，我在等了半小时后没有结果，），具体代码如下；

冒泡排序：

package three.suanfa.whp;import java.io.BufferedReader;import java.io.File;import java.io.FileOutputStream;import java.io.FileReader;import java.io.IOException;import java.util.ArrayList;public class bubbleSort {/** * @王海平 */public static void main(String[] args) {// TODO 自动生成的方法存根double start_all = System.currentTimeMillis();String path = "txt/largeW.txt";ArrayList<Integer> list = read(path);int temp;double start = System.currentTimeMillis();for (int i = 0; i < list.size(); i++) {for (int j = i; j < list.size(); j++) {if (list.get(i) > list.get(j)) {temp = list.get(i);list.set(i, list.get(j));list.set(j, temp);}}}double end = System.currentTimeMillis();System.out.println("冒泡排序时间为: " + (end - start)+"毫秒");// 写入txt文件write(list);System.out.println("写入完成");double end_all = System.currentTimeMillis();System.out.println("总运行时间为: " + (end_all - start_all)+"毫秒");}//创建并写入largeW_bubble.txt文件public static void write(ArrayList list) {File f = new File("txt/largeW_bubble.txt");FileOutputStream fou = null;try {fou = new FileOutputStream(f, true);// true,设置可追加for (int i = 0; i < list.size(); i++) {String s = list.get(i).toString();String a = "" + s + "\t\n";// byte []bytes=new byte[1024];// 如何把string转换byte数组fou.write(a.getBytes());}} catch (Exception e) {// TODO: handle exceptione.printStackTrace();} finally {try {fou.close();} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}//读取文件到Arraylist 数组public static ArrayList read(String path) {ArrayList<Integer> list = new ArrayList<Integer>();BufferedReader input = null;try {FileReader in = new FileReader(path);input = new BufferedReader(in);String ss;try {while ((ss = input.readLine()) != null) {String[] s = ss.split("\r\n");for (int i = 0; i < s.length; i++) {list.add(Integer.parseInt(s[i].trim())); // 将String s中的内容添加到动态数组中}}} catch (IOException e) {// TODO 自动生成的 catch 块e.printStackTrace();}in.close();input.close();} catch (Exception e) {// TODO 自动生成的 catch 块e.printStackTrace();}return list;}}

运行结果：

归并排序：

package three.suanfa.whp;import java.io.BufferedReader;import java.io.File;import java.io.FileOutputStream;import java.io.FileReader;import java.io.IOException;import java.util.ArrayList;public class mergeSort {/** * @王海平 */public static void main(String[] args) {// TODO 自动生成的方法存根double start_all = System.currentTimeMillis();String path = "txt/largeW.txt";ArrayList<Integer> list=read(path); double start = System.currentTimeMillis();mergeSort(list);double end = System.currentTimeMillis();System.out.println("归并排序时间为: " + (end - start)+"毫秒");// 写入txt文件write(list);System.out.println("写入完成");double end_all = System.currentTimeMillis();System.out.println("总运行时间为: " + (end_all - start_all)+"毫秒");}//创建并写入largeW_merge.txt文件public static void write(ArrayList<Integer> list) {File f = new File("txt/largeW_merge.txt");FileOutputStream fou = null;try {fou = new FileOutputStream(f, true);// true,设置可追加for (int i = 0; i < list.size(); i++) {String s = String.valueOf(list.get(i));String a = "" + s + "\t\n";// byte []bytes=new byte[1024];// 如何把string转换byte数组fou.write(a.getBytes());}} catch (Exception e) {// TODO: handle exceptione.printStackTrace();} finally {try {fou.close();} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}//归并排序public static void mergeSort(ArrayList<Integer> data) {          sort(data, 0, data.size() - 1);      }        public static void sort(ArrayList<Integer> data, int left, int right) {          if (left >= right)              return;          // 找出中间索引          int center = (left + right) / 2;          // 对左边数组进行递归          sort(data, left, center);          // 对右边数组进行递归          sort(data, center + 1, right);          // 合并          merge(data, left, center, right);            }          public static void merge(ArrayList<Integer> data, int left, int center, int right) {          // 临时数组          int[] tmpArr = new int[data.size()];          // 右数组第一个元素索引          int mid = center + 1;          // third 记录临时数组的索引          int third = left;          // 缓存左数组第一个元素的索引          int tmp = left;          while (left <= center && mid <= right) {              // 从两个数组中取出最小的放入临时数组              if (data.get(left) <= data.get(mid)) {                  tmpArr[third++] = data.get(left++);              } else {                  tmpArr[third++] = data.get(mid++);              }          }          // 剩余部分依次放入临时数组（实际上两个while只会执行其中一个）          while (mid <= right) {              tmpArr[third++] = data.get(mid++);          }          while (left <= center) {              tmpArr[third++] = data.get(left++);          }          // 将临时数组中的内容拷贝回原数组中          // （原left-right范围的内容被复制回原数组）          while (tmp <= right) {        data.set(tmp, tmpArr[tmp++]);        }      }  //读取文件到int数组public static ArrayList read(String path) {ArrayList<Integer> list = new ArrayList<Integer>();BufferedReader input = null;try {FileReader in = new FileReader(path);input = new BufferedReader(in);String ss;try {while ((ss = input.readLine()) != null) {String[] s = ss.split("\r\n");for (int i = 0; i < s.length; i++) {list.add(Integer.parseInt(s[i].trim())); // 将String s中的内容添加到动态数组中}}} catch (IOException e) {// TODO 自动生成的 catch 块e.printStackTrace();}in.close();input.close();} catch (Exception e) {// TODO 自动生成的 catch 块e.printStackTrace();}return list;}}

运行结果：

排序结果一样：

总结：从上面的排序时间来说，归并排序的时间明显比冒泡排序用的时间少！经查资料（数据结构）得知，归并排序是一种比较稳定的排序方法！

总的时间代价是O(nlog2n),而冒泡排序的时间是O(n的二次方)