算法——【鏈表】——單鏈表面試題

1.求單鏈表中有效結點的個數（新浪）

    //獲取單鏈表結點的個數
    public static int getLength(HeroNode head){

        //如果鏈表爲空
        if (head.next == null){
            return 0;
        }
        //定義長度
        int length = 0;

        HeroNode cur = head.next;
        while(cur != null){
            length++;
            cur = cur.next;
        }
        return length;
    }

2.求單鏈表中倒數第k個結點（新浪）

    //查找單鏈表倒數第k個結點
    //1.獲取單鏈表長度length
    //2.遍歷length-k次即可
    public static HeroNode findLastIndexNode(HeroNode head,int index){
        if (head.next == null){
            return null;
        }
        int length = getLength(head);
        if (index < 0 || index > length){
            return null;
        }
        HeroNode cur = head.next;
        for (int i = 0; i < length-index; i++) {
            cur = cur.next;
        }
        return cur;
    }

3.單鏈表的反轉（騰訊）

    //單鏈表的反轉
    public void reverseList(HeroNode head){
        //如果爲空，或者只有1個結點時，不需要反轉
        if (head.next == null || head.next.next ==null){
            return;
        }
        //工作指針
        HeroNode cur = head.next;
        //工作指針的下一個
        HeroNode next = null;

        HeroNode reverseHead = new HeroNode(0,"","");
        while(cur != null){
            next = cur.next;
            cur.next = reverseHead.next;
            reverseHead.next = cur;
            cur = next;
        }
        //將head的next指向reverseHead的next，實現反轉
        head.next = reverseHead.next;
    }

4.從尾到頭打印單鏈表（百度）

    //從尾到頭打印單鏈表
    //1.先進後出=>棧
    public void reversePrint(HeroNode head){
        if (head.next == null){
            return;
        }
        Stack<HeroNode> stack = new Stack<>();
        HeroNode cur = head.next;
        while (cur != null){
            stack.push(cur);
            cur = cur.next;
        }
        //棧內大於0
        while(stack.size() > 0){
            System.out.println(stack.pop());
        }
    }

5.合併兩個有序單鏈表

    //合併兩個有序的單鏈表
    //1.判斷兩個單鏈表哪個小，小的加入
    //2.添加兩個單鏈表最後剩下的
    public static HeroNode mergeLinkedList(HeroNode head1,HeroNode head2){
        //創建新的頭結點
        HeroNode newHead = new HeroNode(0,"","");
        //尾指針
        HeroNode rear = newHead;
        if (head1.next == null){
            newHead.next = head2.next;
            return newHead;
        }
        if (head2.next == null){
            newHead.next = head1.next;
            return newHead;
        }
        //兩個鏈表的工作指針
        HeroNode cur1 = head1.next;
        HeroNode next1 = null;
        HeroNode cur2 = head2.next;
        HeroNode next2 = null;

        //當鏈表1和2都不到尾部時
        while(cur1 != null && cur2 != null){
            //判斷大小
            if (cur1.no < cur2.no){
                //後指針
                next1 = cur1.next;

                //插入位置，尾指針後移
                cur1.next = rear.next;
                rear.next = cur1;
                rear = cur1;

                //工作指針迴歸
                cur1 = next1;
            }
            else{
                //後指針
                next2 = cur2.next;

                //插入位置，尾指針後移
                cur2.next = rear.next;
                rear.next = cur2;
                rear = cur2;

                //工作指針迴歸
                cur2 = next2;
            }
        }

        //添加剩餘的鏈表
        while(cur1 != null){
            next1 = cur1.next;
            cur1.next = rear.next;
            rear.next = cur1;
            cur1 = next1;
        }

        while(cur2 != null){
            next2 = cur2.next;
            cur2.next = rear.next;
            rear.next = cur2;
            cur2 = next2;
        }

        return newHead;
    }