SetOperation.java

package com.study.collection;

import java.util.ArrayList;
import java.util.Arrays;

/*
ArrayList를 이용한 집합 연산
 */

class StringSet {

  ArrayList<String> list = new ArrayList<String>();

  public void add(String s) {
    list.add(s);
  }

  public void remove(String s) {
    list.remove(s);
  }

  public boolean contains(String s) {
    return list.contains(s);
  }

  public StringSet union(StringSet set) {
    StringSet newSet = new StringSet();
    newSet.list.addAll(this.list);
    newSet.list.removeAll(set.list);
    newSet.list.addAll(set.list);
    return newSet;
  }

  public StringSet intersection(StringSet set) {
    StringSet newSet = new StringSet();
    newSet.list.addAll(this.list);
    newSet.list.retainAll(set.list);
    return newSet;
  }

  public StringSet difference(StringSet set) {
    StringSet newSet = new StringSet();
    newSet.list.addAll(this.list);
    newSet.list.removeAll(set.list);
    return newSet;
  }

  @Override
  public boolean equals(Object obj) {
    if (obj instanceof StringSet == false) return false;
    StringSet set = (StringSet) obj;
    return this.list.equals(set.list);
  }

  public String[] toArray() {
    return list.toArray(new String[0]);
  }

}

public class SetOperation {

  static void print(String msg, StringSet set) {
    String[] a = set.toArray();
    Arrays.sort(a);
    String temp = Arrays.toString(a);
    System.out.printf("%s: %s\n", msg, temp);
  }

  public static void main(String[] args) {

    StringSet A = new StringSet();
    for (int i = 0; i < 20; ++i) {
      String s = String.format("%02d", i);
      A.add(s);
    }
    print("A", A);

    StringSet B = new StringSet();
    for (int i = 0; i < 20; i += 2) {
      String s = String.format("%02d", i);
      B.add(s);
    }
    print("B", B);

    StringSet C = new StringSet();
    for (int i = 0; i < 20; i += 3) {
      String s = String.format("%02d", i);
      C.add(s);
    }
    print("C", C);

    print("A 합집합 B", A.union(B));
    print("A 교집합 B", A.intersection(B));
    print("A 합집합 C", A.union(C));
    print("A 교집합 C", A.intersection(C));
    print("B 합집합 C", B.union(C));
    print("B 교집합 C", B.intersection(C));
    print("A 차집합 B", A.difference(B));
  }

}