Remove Duplicates from Sorted List
描述
Given a sorted linked list, delete all duplicates such that each element appear only once.
For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.
分析
无
递归版
// Remove Duplicates from Sorted List
// 递归版，时间复杂度O(n)，空间复杂度O(1)
class Solution {
public ListNode deleteDuplicates(ListNode head) {
if (head == null) return head;
ListNode dummy = new ListNode(head.val + 1); // 值只要跟head不同即可
dummy.next = head;
recur(dummy, head);
return dummy.next;
}
private static void recur(ListNode prev, ListNode cur) {
if (cur == null) return;
if (prev.val == cur.val) { // 删除head
prev.next = cur.next;
recur(prev, prev.next);
} else {
recur(prev.next, cur.next);
}
}
};迭代版
// Remove Duplicates from Sorted List
// 迭代版，时间复杂度O(n)，空间复杂度O(1)
class Solution {
public ListNode deleteDuplicates(ListNode head) {
if (head == null) return null;
for (ListNode prev = head, cur = head.next; cur != null; cur = prev.next) {
if (prev.val == cur.val) {
prev.next = cur.next;
} else {
prev = cur;
}
}
return head;
}
};