LinkedHashSet_重複號碼

xkfx發表於2024-12-06

問題描述

已知陣列存放一批QQ號碼，QQ號碼最長為11位，最短為5位 String[] strs = {"12345","67891","12347809933","98765432102","67891","12347809933"}。 將該陣列裡面的所有qq號都存放在LinkedList中，將list中重複的元素刪除，將list中所有元素分別用迭代器和增強for迴圈列印出來。

參考思路

1 將陣列中的所有qq號存放在LinkedList中

import java.util.LinkedList;
import java.util.List;

public class Main {

    public static void main(String[] args) {
        String[] strings = {"12345","67891","12347809933","98765432102","67891","12347809933"};

        List<String> list = new LinkedList<>();

        for (String s : strings) {
            list.add(s); 
        }

        System.out.println(list);
    }
}

把陣列裡的元素新增到一個集合類中，存在一種簡潔的寫法——使用Collections類中定義的addAll方法。如果檢視原始碼，會發現它其實也是去使用了foreach迴圈，因此可以理解上述寫法的縮寫形式。

    @SafeVarargs
    public static <T> boolean addAll(Collection<? super T> c, T... elements) {
        boolean result = false;
        for (T element : elements)
            result |= c.add(element);
        return result;
    }

透過addAll方法上述程式碼可以簡化為：

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

public class Main {

    public static void main(String[] args) {
        // 已知陣列存放了一批qq號
        String[] strings = {"12345","67891","12347809933","98765432102","67891","12347809933"};

        // 1 將陣列中所有qq號都存放在LinkedList裡面
        List<String> list = new LinkedList<>();

        Collections.addAll(list, strings);

        System.out.println(list);
        // => [12345, 67891, 12347809933, 98765432102, 67891, 12347809933]
    }
}

PS. 實際編碼時可經常性地輸出中間變數進行除錯，而不是一定要寫完程式碼才執行！

2 將list中重複的元素刪除

存在多種思路（人工刪除list中重複元素相對繁瑣），這裡採用一種更簡潔的辦法——透過LinkedHashSet清除list中的重複元素

import java.util.*;

public class Main {
    public static void main(String[] args) {
        String[] strings = {"12345","67891","12347809933","98765432102","67891","12347809933"};
        List<String> list = new LinkedList<>();
        Collections.addAll(list, strings);
//        System.out.println(list);
        // => [12345, 67891, 12347809933, 98765432102, 67891, 12347809933]
        Set<String> set = new LinkedHashSet<>(list);
        list.clear();
        list.addAll(set);
        System.out.println(list);
        // => [12345, 67891, 12347809933, 98765432102, 67891, 12347809933]
    }
}

3 分別用迭代器和增強for迴圈列印list中所有元素

import java.util.*;

public class Main {
    public static void main(String[] args) {
        String[] strings = {"12345","67891","12347809933","98765432102","67891","12347809933"};
        List<String> list = new LinkedList<>();
        Collections.addAll(list, strings);
//        System.out.println(list);
        // => [12345, 67891, 12347809933, 98765432102, 67891, 12347809933]
        Set<String> set = new LinkedHashSet<>(list);
        list.clear();
        list.addAll(set);
//        System.out.println(list);
        // => [12345, 67891, 12347809933, 98765432102]
        System.out.println("迭代器:");
        Iterator ite = list.iterator();
        while (ite.hasNext()) {
            System.out.print(ite.next() + " ");
        }

        System.out.println("\n增強for:");
        for (String s : list) {
            System.out.print(s + " ");
        }
    }
}

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