LeetCode Remove Nth Node From End of List C++

最新推荐文章于 2020-06-19 22:40:41 发布

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本文介绍了一种高效的算法，用于从链表中删除倒数第N个节点。该方法仅需遍历一次链表即可完成操作，通过使用两个指针，巧妙地定位待删除节点的位置。

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#include <iostream>
#include <vector>
#include<algorithm>
#include <queue>
using namespace std;

/************************************************************************/
/* 
    Problem:
    Given a linked list, remove the nth node from the end of list and return its head.

For example,

   Given linked list: 1->2->3->4->5, and n = 2.

   After removing the second node from the end, the linked list becomes 1->2->3->5.
Note:
    Given n will always be valid.
    Try to do this in one pass.

    Author  :   crazys_popcorn@126.com

    DateTime:   2017年8月9日 13:28:52

*/
/************************************************************************/





struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {


        if (head == NULL )
            return  head;

        ListNode *current = NULL;
        ListNode *frist = head;
        ListNode *second = head;
        //n需要见 -1 记录出当前的前一个位置。以便于获取指针
        for (int i = 0; i < n-1; i++)
        {
            second = second->next;
        }

        while (second->next)
        {
            current = frist;  //记录前一个指针
            frist = frist->next;
            second = second->next;      
        }
        if (current == nullptr)
        {
            head = frist->next;
            delete frist;
        }
        else
        {
            //衔接。删除frist  并把 frist 的下一级衔接到 frist的上一级
            current->next = frist->next;
            delete frist;
        }
        return head;


    }
};

void main()
{

    ListNode *t1 = new ListNode(0);
    ListNode *t2 = new ListNode(0);
    ListNode *t3 = new ListNode(0);
    ListNode *t4 = new ListNode(0);
    t1->val = 1;
    t2->val = 2;
    t3->val = 3;
    t4->val = 4;
    t1->next = t2;
    t2->next = t3;
    t3->next = t4;
    Solution s1;
    s1.removeNthFromEnd(t1, 2);
    system("pause");
    return ;
}