如何在Java中从ArrayList中删除重复对？

Question

class Pair<t1,t2>
{
    int i, j;
    Pair(int i,int j){
        this.i=i;
        this.j=j;
    }

}

public class My 
{
    public static void main(String[] args) {
        Pair p;
        List<Pair<Integer,Integer>> src = Arrays.asList(new Pair(1,2), 
            new Pair(2,3), new Pair(2,1),new Pair(1,2));
        HashSet<String> dest  = new HashSet();

        for(int i=0; i < src.size(); i++) {
            p=src.get(i);
            if(dest.contains(p.j+" "+p.i)) {
                System.out.println("duplicacy");
            }  
            else {
                dest.add(p.i+" "+p.j);
            }
         
        }
        System.out.println("set is = "+dest);
     
        List<Pair<Integer,Integer>> ans=new ArrayList();
        String temp;
        int i,j;
        Iterator<String> it=dest.iterator();
        while(it.hasNext()) 
        {
            temp=it.next();
            i=Integer.parseInt(temp.substring(0,temp.indexOf(' ')));
            j=Integer.parseInt(temp.substring(temp.indexOf(' 
               ')+1,temp.length()));
            ans.add(new Pair(i,j));
         }
    
         for(Pair i_p:ans) {
             System.out.println("Pair = "+i_p.i+" , "+i_p.j);
         }

     }//end of main method
 }//end of class My

这段代码运行良好，但我想知道它的性能，我指的是它的总体时间复杂度？

Answer 1

>

如果可以修改pair类，只需实现equals()和hashcode():

public class Pair {
    private int a;
    private int b;

    public Pair(int a, int b) {
        this.a = a;
        this.b = b;
    }

    @Override
    public boolean equals(Object o) { 
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Pair pair = (Pair) o;
        return (a == pair.a && b == pair.b) || (a == pair.b && b == pair.a);
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(new HashSet<>(Arrays.asList(a,b))); 
    }

    @Override
    public String toString() {
        return "Pair{" +
                "a=" + a +
                ", b=" + b +
                '}';
    }
}

然后只需创建一个新的集 :

List<Pair> pairs = Arrays.asList(new Pair(1, 2), new Pair(2, 1), new Pair(3, 2));

Set<Pair> pairSet = new HashSet<>(pairs);

System.out.println(pairSet);

输出：

[Pair{a=1, b=2}, Pair{a=3, b=2}]

List<Pair> pairs = Arrays.asList(new Pair(1, 2), new Pair(2, 1), new Pair(3, 2));

Set<Pair> pairSet = pairs.stream()
      .map(pair -> new HashSet<>(Arrays.asList(pair.getA(), pair.getB())))
      .distinct()
      .map(integers -> {
          Iterator<Integer> iterator = integers.stream().iterator();
          return new Pair(iterator.next(), iterator.next());
      })
      .collect(Collectors.toSet());

System.out.println(pairSet);

[Pair{a=1, b=2}, Pair{a=2, b=3}]

List<Pair> list = new ArrayList<>(set);