24. 兩兩交換鏈表中的節(jié)點

思想：重點在于如何交換兩個節(jié)點，順序如圖所示：

交換兩個節(jié)點.png

/**
 * 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 swapPairs(ListNode head) {
        ListNode dummy = new ListNode(-1,head);
        ListNode prev = dummy;
        while(prev.next != null && prev.next.next != null){
            ListNode temp = head.next.next;
            prev.next = head.next;
            head.next.next = head;
            head.next = temp;
            prev = head;
            head = head.next;
        }
        return dummy.next;
    }
}

19.刪除鏈表的倒數(shù)第N個節(jié)點

思路：雙指針的典型應(yīng)用。

面試題 02.07. 鏈表相交

142.環(huán)形鏈表II