Remove Duplicates from Sorted List
Given a sorted linked list, delete all duplicates such that each element appear only once.
Example 1:
Input: 1->1->2
Output: 1->2
Example 2:
Input: 1->1->2->3->3
Output: 1->2->3
思路一：迭代
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
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;
}
};
时间复杂度o(n),空间复杂度o(1)
思路二：递归
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);
}
}
};
时间复杂度o(n),空间复杂度o(1)