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Remove Duplicates from Sorted List II

描述

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,

Given 1->2->3->3->4->4->5, return 1->2->5.

Given 1->1->1->2->3, return 2->3.

分析

递归版

// Remove Duplicates from Sorted List II
// 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 || head.next == null) return head;

ListNode slow = head;
ListNode fast = head.next;
if (slow.val == fast.val) {
while (fast != null && slow.val == fast.val) {
fast = fast.next;
}
return deleteDuplicates(fast);
} else {
slow.next = deleteDuplicates(slow.next);
return slow;
}
}
};

迭代版

// Remove Duplicates from Sorted List II
// 迭代版,时间复杂度O(n),空间复杂度O(1)
public class Solution {
public ListNode deleteDuplicates(ListNode head) {
if (head == null) return head;

ListNode dummy = new ListNode(Integer.MAX_VALUE); // 头结点
dummy.next = head;
ListNode prev = dummy, cur = head;
while (cur != null) {
boolean duplicated = false;
while (cur.next != null && cur.val == cur.next.val) {
duplicated = true;
cur = cur.next;
}
if (duplicated) { // 删除重复的最后一个元素
cur = cur.next;
continue;
}
prev.next = cur;
prev = prev.next;
cur = cur.next;
}
prev.next = cur;
return dummy.next;
}
}

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