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

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;
    }
};

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