时间复杂度

对一个数组去重
用list实现复杂度为O(n的平方)

    public  static List getDistinctArray(Integer[] a){
        List arraySame = new ArrayList();
        arraySame.add(a[0]);
        boolean flag;
        for(int i=1;i

用Set实现复杂度为O(n)

        String[] array = {"a","b","c","c","d","e","e","e","a"};  
        Set set = new HashSet<>();  
        for(int i=0;i

比较两个数组相同与差异

package com.fei.maintest;

import java.util.*;

public class SetTest {

    public static void main(String[] args) {

        Integer[] array1 = {1,2,3,4,1,2,4,6,7,8,30,22,33};
        Integer[] array2 = {1,2,3,4,1,2,4,6,7,8,30,22,33,55,66,77};

        Set sameElementSet = getSameBySet(array1,array2);
        System.out.println("\ngetSame by Set:");
        for(Integer i : sameElementSet)
            System.out.print(i+",");

        List sameElementList = getSameByArray(array1,array2);
        System.out.println("\ngetSame by List:");
        for (int i=0;i list = compare(array1,array2);
        System.out.println("\narray2 compare array1:");
        for (Integer integer : list)
            System.out.print(integer+",");

    }

    public  static List getSameByArray(Integer[] a, Integer[] b){
        List listA = getDistinctArray(a);
        List listB = getDistinctArray(b);
        List arraySame = new ArrayList();
        for(int i=0;i getSameBySet(Integer[] a, Integer[] b){
        Set same = new HashSet();  //用来存放两个数组中相同的元素
        Set temp = new HashSet();  //用来存放数组a中的元素

        for (int i = 0; i < a.length; i++) {
            temp.add(a[i]);   //把数组a中的元素放到Set中，可以去除重复的元素
        }

        System.out.println("temp:");
        Iterator it = temp.iterator();
        while (it.hasNext()) {
            System.out.print(it.next()+",");
        }

        for (int j = 0; j < b.length; j++) {
            //把数组b中的元素添加到temp中
            //如果temp中已存在相同的元素，则temp.add（b[j]）返回false
            if(!temp.add(b[j]))
                same.add(b[j]);
        }
        return same;
    }

    public static  List compare(T[] t1, T[] t2) {
        List list1 = Arrays.asList(t1);
        List list2 = new ArrayList();
        for (T t : t2) {
            if (!list1.contains(t)) {
                list2.add(t);
            }
        }
        return list2;
    }


    public  static List getDistinctArray(Integer[] a){
        List arraySame = new ArrayList();
        arraySame.add(a[0]);
        boolean flag;
        for(int i=1;i

输出

temp:
1,33,2,3,4,6,22,7,8,30,
getSame by Set:
1,33,2,3,4,6,22,7,8,30,
getSame by List:
1,2,3,4,6,7,8,30,22,33,
array2 compare array1:
55,66,77,

如果传入的两个数组有重复

package com.fei.maintest;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.*;

public class ReadfileTest {

    public static void main(String[] args) {

        String fileName = "/Users/bestfei/Downloads/url.txt";
        String fileNameB = "/Users/bestfei/Downloads/url2.txt";
        //readFileByLines(fileName);
        List a = getFileArrayListByLines(fileName);
        List b = getFileArrayListByLines(fileNameB);
        System.out.println("getSameBySet");
        getSameBySet(getDistinctSet(a),getDistinctSet(b));
        System.out.println("getSameByArrayList");
        getSameByArrayList(getDistinctArrayList(a),getDistinctArrayList(b));
    }

    public static void getSameByArrayList(List a,List b){
        ArrayList l = new ArrayList();
        for(int i=0;i

参考文档：
http://blog.csdn.net/xiaoxiaopengbo/article/details/51583386
http://blog.csdn.net/qq_33642117/article/details/52040345