Leetcode 19. Remove Nth Node From End of List

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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.

题目大意：删除链表中倒数第n个节点。

题目分析：使用双指针相聚n-1，当第二个指针遍历到链表尾部则第一个指针就是要删除的节点指针。这里有个问题，因为要删除节点，所以不添加头结点的话，要把删除第一个节点，和其他节点区分开来（第一个节点没有前驱）。如果添加则可以统一处理。下面分别是两种代码，运行时间都是4ms

方法一（不添加头节点）：

/**
 * Definition for singly-linked list.
 * 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||head->next==NULL) return NULL;
        ListNode* first=head;
        ListNode* second=head;
        for(int i=0;i<n-1;i++)
            second=second->next;
        if(second->next==NULL){//删除第一个节点
            head=head->next;
            return head;
        }
        while(second->next->next){
            second=second->next;
            first=first->next;
        }
        first->next=first->next->next;
        return head;
    }
};

/**
 * Definition for singly-linked list.
 * 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 NULL;
        ListNode h(INT_MAX);
        h.next=head;
        
        ListNode *pfirst=&h;
        ListNode *psecond=&h;
        ListNode *temp;//释放被删除的空间
        
        for(int i=0;i<n;i++)
            psecond=psecond->next;
        while(psecond->next){
            psecond=psecond->next;
            pfirst=pfirst->next;
        }
        temp=pfirst->next;
        pfirst->next=pfirst->next->next;
        delete temp;
        return h.next;
    }
};

Leetcode 19. Remove Nth Node From End of List

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原文地址：http://blog.csdn.net/a2415180498/article/details/51352147