第三周作业——冒泡排序和归并排序

最新推荐文章于 2020-02-23 21:47:08 发布

孙凌峰_

最新推荐文章于 2020-02-23 21:47:08 发布

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本文链接：https://blog.youkuaiyun.com/u014007551/article/details/22322981

本文通过实验对比了归并排序与冒泡排序的效率，使用Java实现这两种排序算法，并对从文件中读取的数据进行排序，记录并比较它们所需的时间。结果表明，归并排序明显优于冒泡排序。

import java.io.*;
import java.util.*;

public class Sort {

	public void bubbleSort(ArrayList list) {
		for (int i = 0; i < list.size(); i++) {
			for (int j = i + 1; j < list.size(); j++) {
				if (list.get(i) > list.get(j)) {
					int temp = list.get(i);
					list.set(i, list.get(j));
					list.set(j, temp);
				}
			}
		}
		for (int i = 0; i < list.size(); i++) {
			System.out.println(list.get(i));
		}
	}

	public void merge(int[] a, int s, int m, int t) {
		int[] tmp = new int[t - s + 1];
		int i = s, j = m, k = 0;
		while (i < m && j <= t) {
			if (a[i] <= a[j]) {
				tmp[k] = a[i];
				k++;
				i++;
			} else {
				tmp[k] = a[j];
				j++;
				k++;
			}
		}
		while (i < m) {
			tmp[k] = a[i];
			i++;
			k++;
		}

		while (j <= t) {
			tmp[k] = a[j];
			j++;
			k++;
		}
		System.arraycopy(tmp, 0, a, s, tmp.length);
	}

	public void mergeSort(int[] a, int s, int len) {
		int size = a.length;
		int mid = size / (len << 1);
		int c = size & ((len << 1) - 1);
		if (mid == 0)
			return;
		for (int i = 0; i < mid; ++i) {
			s = i * 2 * len;
			merge(a, s, s + len, (len << 1) + s - 1);
		}
		if (c != 0)
			merge(a, size - c - 2 * len, size - c, size - 1);
		mergeSort(a, 0, 2 * len);
	}

	public static void main(String[] args) {
		File file1 = new File("largeW.txt");
		File file2 = new File("largeW_bubble.txt");
		File file3 = new File("largeW_merge.txt");
		ArrayList list = new ArrayList();

		// 读取数据
		try {
			FileReader in = new FileReader(file1);
			BufferedReader bufr = new BufferedReader(in);
			String s = null;
			int t;
			while ((s = bufr.readLine()) != null) {
				t = Integer.parseInt(s.trim());
				list.add(t);
			}
			bufr.close();
			in.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		Sort sort = new Sort();
		long startsysDate = System.currentTimeMillis();
		sort.bubbleSort(list);
		long endsysDate = System.currentTimeMillis();
		System.out.println(endsysDate - startsysDate);

		try {
			FileOutputStream fos = new FileOutputStream(file2);
			OutputStreamWriter osw = new OutputStreamWriter(fos, "gb2312");
			BufferedWriter bw = new BufferedWriter(osw);
			for (int i = 0; i < list.size(); i++) {
				bw.write(list.get(i).toString());
				bw.newLine();
			}
			bw.close();
			osw.close();
			fos.close();
		} catch (FileNotFoundException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (UnsupportedEncodingException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (IOException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}

		int[] a = new int[list.size()];
		for (int i = 0; i < list.size(); i++) {
			a[i] = list.get(i);
		}
		startsysDate = System.currentTimeMillis();
		sort.mergeSort(a, 0, 1);
		endsysDate = System.currentTimeMillis();
		System.out.println(endsysDate - startsysDate);
		try {
			FileOutputStream fos = new FileOutputStream(file3);
			OutputStreamWriter osw = new OutputStreamWriter(fos, "gb2312");
			BufferedWriter bw = new BufferedWriter(osw);
			String str;
			for (int i = 0; i < list.size(); i++) {
				str = Integer.toString(a[i]);
				bw.write(str);
				bw.newLine();
			}
			bw.close();
			osw.close();
			fos.close();
		} catch (FileNotFoundException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (UnsupportedEncodingException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (IOException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
	}
}

由于冒泡排序用了35767251毫秒，而归并排序只用了93毫秒、、发现归并排序用了已经排好序了的数组，于是将冒泡排序注释掉

import java.io.*;
import java.util.*;

public class Sort {

	public void bubbleSort(ArrayList list) {
		for (int i = 0; i < list.size(); i++) {
			for (int j = i + 1; j < list.size(); j++) {
				if (list.get(i) > list.get(j)) {
					int temp = list.get(i);
					list.set(i, list.get(j));
					list.set(j, temp);
				}
			}
		}
		for (int i = 0; i < list.size(); i++) {
			System.out.println(list.get(i));
		}
	}

	public void merge(int[] a, int s, int m, int t) {
		int[] tmp = new int[t - s + 1];
		int i = s, j = m, k = 0;
		while (i < m && j <= t) {
			if (a[i] <= a[j]) {
				tmp[k] = a[i];
				k++;
				i++;
			} else {
				tmp[k] = a[j];
				j++;
				k++;
			}
		}
		while (i < m) {
			tmp[k] = a[i];
			i++;
			k++;
		}

		while (j <= t) {
			tmp[k] = a[j];
			j++;
			k++;
		}
		System.arraycopy(tmp, 0, a, s, tmp.length);
	}

	public void mergeSort(int[] a, int s, int len) {
		int size = a.length;
		int mid = size / (len << 1);
		int c = size & ((len << 1) - 1);
		if (mid == 0)
			return;
		for (int i = 0; i < mid; ++i) {
			s = i * 2 * len;
			merge(a, s, s + len, (len << 1) + s - 1);
		}
		if (c != 0)
			merge(a, size - c - 2 * len, size - c, size - 1);
		mergeSort(a, 0, 2 * len);
	}

	public static void main(String[] args) {
		File file1 = new File("largeW.txt");
		File file2 = new File("largeW_bubble.txt");
		File file3 = new File("largeW_merge.txt");
		ArrayList list = new ArrayList();

		// 读取数据
		try {
			FileReader in = new FileReader(file1);
			BufferedReader bufr = new BufferedReader(in);
			String s = null;
			int t;
			while ((s = bufr.readLine()) != null) {
				t = Integer.parseInt(s.trim());
				list.add(t);
			}
			bufr.close();
			in.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		Sort sort = new Sort();
		/*long startsysDate = System.currentTimeMillis();
		sort.bubbleSort(list);
		long endsysDate = System.currentTimeMillis();
		System.out.println(endsysDate - startsysDate);*/

		try {
			FileOutputStream fos = new FileOutputStream(file2);
			OutputStreamWriter osw = new OutputStreamWriter(fos, "gb2312");
			BufferedWriter bw = new BufferedWriter(osw);
			for (int i = 0; i < list.size(); i++) {
				bw.write(list.get(i).toString());
				bw.newLine();
			}
			bw.close();
			osw.close();
			fos.close();
		} catch (FileNotFoundException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (UnsupportedEncodingException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (IOException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}

		int[] a = new int[list.size()];
		for (int i = 0; i < list.size(); i++) {
			a[i] = list.get(i);
		}
		long startsysDate = System.currentTimeMillis();
		sort.mergeSort(a, 0, 1);
		long endsysDate = System.currentTimeMillis();
		System.out.println(endsysDate - startsysDate);
		try {
			FileOutputStream fos = new FileOutputStream(file3);
			OutputStreamWriter osw = new OutputStreamWriter(fos, "gb2312");
			BufferedWriter bw = new BufferedWriter(osw);
			String str;
			for (int i = 0; i < list.size(); i++) {
				str = Integer.toString(a[i]);
				bw.write(str);
				bw.newLine();
			}
			bw.close();
			osw.close();
			fos.close();
		} catch (FileNotFoundException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (UnsupportedEncodingException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		} catch (IOException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
	}
}

发现差别不是很大…………