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Dummy????

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Dummy?????

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class ListNode {
    public int val;
    public ListNode next;
    public ListNode(int value) {
        val = value;
    }
}

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  ??????next?????null?

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public class LinkedList {
    private ListNode dummy;
    public LinkedList() {
        dummy = new ListNode(-1);
    }
}

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  ?????dummy??????????????????

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1. ????

public void add(int location, int val) {
    ListNode pre = dummy;
    for (int i = 0; i < location; i++) {
        pre = pre.next;
    }
    ListNode node = new ListNode(val);
    node.next = pre.next;
    pre.next = node;
}

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  ???0?????????????????????

2. ????

public void remove(int location) {
    ListNode pre = dummy;
    for (int i = 0; i < location; i++) {
        pre = pre.next;
    }
    pre.next = pre.next.next;
}

• ????
  ???????????????next????????

3. ????

public int get(int location) {
    ListNode cur = dummy.next;
    for (int i = 0; i < location; i++) {
        cur = cur.next;
    }
    return cur.val;
}

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  ?????????????????

4. ????

public boolean contain(int val) {
    ListNode cur = dummy.next;
    while (cur != null) {
        if (cur.val == val) {
            return true;
        }
        cur = cur.next;
    }
    return false;
}

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  ?dummy??????????????????????????

5. ????

public void print() {
    ListNode cur = dummy.next;
    while (cur != null) {
        System.out.print(cur.val + "->");
        cur = cur.next;
    }
    System.out.println("null");
}

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  ????????????null????????

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public static void main(String[] args) {
    LinkedList list = new LinkedList();
    list.add(0, 10);
    list.add(1, 20);
    list.add(2, 40);
    list.remove(1);
    list.print();
    System.out.println(list.get(0));
    System.out.println(list.get(1));
    System.out.println(list.contain(50));
    System.out.println(list.contain(40));
}

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ArrayList?LinkedList???????

LeetCode????

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• Solution???

  LeetCode????Solution??????????????????

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  ??main???????????????????

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