1.删除指定元素

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {
        ListNode dummyHead = new ListNode(0);
        dummyHead.next = head;
        ListNode p = dummyHead;
        while(p.next!=null){
            if(p.next.val==val) p.next=p.next.next;
            else p = p.next;
        }
        return dummyHead.next;
    }
}

2.设计链表

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

}
class MyLinkedList {

    int size;
    ListNode head;

    public MyLinkedList() {
        size = 0;
        head = new ListNode(0); 
    }

    public int get(int index) {
        if(index<0||index>=size){
            return -1;
        }
        ListNode cur = head;
        for(int i=0;i<=index;i++) cur = cur.next;
        return cur.val;

    }

    public void addAtHead(int val) {
        addAtIndex(0,val);
    }

    public void addAtTail(int val) {
        addAtIndex(size,val);
    }

    public void addAtIndex(int index, int val) {
        if(index>size) return;
        index = Math.max(0,index);
        size++;
        ListNode pred = head;
        for(int i=0;i<index;i++) pred = pred.next;
        ListNode toAdd = new ListNode(val);
        toAdd.next = pred.next;
        pred.next = toAdd;

    }

    public void deleteAtIndex(int index) {
        if(index<0 || index>=size) return;
        size--;
        ListNode pred = head;
        for(int i=0;i<index;i++) pred=pred.next;
        pred.next = pred.next.next;

    }
}

/**
 * Your MyLinkedList object will be instantiated and called as such:
 * MyLinkedList obj = new MyLinkedList();
 * int param_1 = obj.get(index);
 * obj.addAtHead(val);
 * obj.addAtTail(val);
 * obj.addAtIndex(index,val);
 * obj.deleteAtIndex(index);
 */

3.反转链表

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode pred = null,cur = head; 
        while(cur!=null){
            ListNode next = cur.next;
            cur.next = pred;
            pred = cur;
            cur = next;
        }
        return pred;
    }
}