linear-list/linked-list/remove-duplicates-from-sorted-list

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);
        }
    }
};

// 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) return head;
        ListNode dummy(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 == nullptr) return;

        if (prev->val == cur->val) { // 删除head
            prev->next = cur->next;
            delete cur;
            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;
    }
};

// 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 == nullptr) return nullptr;

        for (ListNode *prev = head, *cur = head->next; cur != nullptr; cur = prev->next) {
            if (prev->val == cur->val) {
                prev->next = cur->next;
                delete cur;
            } else {
                prev = cur;
            }
        }
        return head;
    }
};

相关题目

• Remove Duplicates from Sorted List II