83. 删除排序链表中的重复元素

递归法

/**
 * 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;
        }
        head.next = deleteDuplicates(head.next);
        if (head.val == head.next.val) {
            head = head.next;
        }
        return head;
    }
}

• 时间复杂度 O(n)
• 空间复杂度 O(n)

迭代法

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode p = head;
        while (p != null && p.next != null) {
            if (p.val == p.next.val) {
                p.next = p.next.next;
            } else {
                p = p.next;
            }
        }
        return head;
    }
}

• 时间复杂度 O(n)
• 空间复杂度 O(1)