剑指18：删除链表中重复的节点

传送门

nowcoder
leetcode

题目描述

在一个排序的链表中，存在重复的结点，请删除该链表中重复的结点，重复的结点不保留，返回链表头指针。
例如，链表 1->2->3->3->4->4->5 处理后为 1->2->5 。

C++ 代码 - nowcoder

/*
	删除链表中重复的结点，重复的结点不保留
    三个指针，取到原来指针的前一个指针
*/
class Solution {
  public:
    ListNode* deleteDuplication(ListNode* pHead) {
        if (pHead == nullptr || pHead->next == nullptr) return pHead;

        ListNode* dummy = new ListNode(-1);
        dummy->next = pHead;
        ListNode* prev = dummy;
        ListNode* cur = dummy->next; // cur 是工作结点
        while (cur != nullptr) {
            if (cur->next != nullptr && cur->val == cur->next->val) {
                while (cur->next != nullptr && cur->val == cur->next->val) {
                    cur = cur->next;
                }
                prev->next = cur->next;
                cur = cur->next;
            } else {
                prev = prev->next;
                cur = cur->next;
            }
        }
        return dummy->next;
    }
};

C++ 代码 - leetcode

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (head == nullptr) return head;

        ListNode* dummy = new ListNode(-1);
        dummy->next = head;
        ListNode* cur = dummy;
        while (cur->next && cur->next->next) {
            if (cur->next->val == cur->next->next->val) {
                int t = cur->next->val;
                while (cur->next && cur->next->val == t) {
                    cur->next = cur->next->next;
                }
            } else {
                cur = cur->next;
            }
        }
        return dummy->next;
    }
};

/*
    变形：删除链表中的重复结点，使每个元素只出现一次 
*/
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (head == nullptr) return head;

        ListNode* cur = head;
        while (cur->next != nullptr) {
            if (cur->val == cur->next->val) {
                cur->next = cur->next->next;
            } else {
                cur = cur->next;
            }
        }
        
        return head;
    }
};

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (head == nullptr) return head;

        ListNode* cur = head;
        for (ListNode* p = head->next; p; p = p->next) {
            if (cur->val != p->val) {
                cur->next = p;
                cur = cur->next;
            }
        }
        cur->next = nullptr;

        return head;
    }
};