链表

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        ListNode h1=headA;
        ListNode h2=headB;
        while(h1!=h2){
            h1=(h1==null)?headB:h1.next;
            h2=(h2==null)?headA:h2.next;
        }
        return h1;
    }
}

 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode cur=head;
        ListNode pre=null;
        ListNode tmp=null;
        while(cur!=null){
            tmp=cur.next;
            cur.next=pre;
            pre=cur;
            cur=tmp;
        }
        return pre;
    }
}

 

/**
 * 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 mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1==null) return l2;
        if(l2==null) return l1;
        if(l1.val

 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head==null||head.next==null) return head;
        // 删除头节点后面挂接的链表中的重复元素
        head.next=deleteDuplicates(head.next); 
        // 头节点与后面挂接的链表中的节点值相同，则头节点也删除，否则不删除
        return head.val==head.next.val?head.next:head;
    }
}

 

/**
在本题中：
返回值：交换完成的子链表
调用单元：设需要交换的两个点为 head 和 node，head 连接后面交换完成的子链表，node 连接 head，完成交换
终止条件：head 为空指针或者 next 为空指针，也就是当前无节点或者只有一个节点，无法进行交换
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        if(head==null||head.next==null) return head;
        ListNode node=head.next;
        head.next=swapPairs(node.next);
        node.next=head;
        return node;
    }
}