19.RemoveNthNodeFromEndofList.cpp

/* 
Given a linked list, remove the n-th node from the end of list and return its head.

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.

Follow up:

Could you do this in one pass? 
*/
/**
 * 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) {
        int num = 0;
        struct ListNode *t = (ListNode *)malloc(sizeof(ListNode));
        t = head;
        while(t->next != NULL){
            ++num;
            t = t->next;
        }

        t = head;
        int m = num - n;
        int p = 0;
        if(m == -1){
            return t->next;
        }
        while(p != m){
            t = t->next;
            ++p;
        }
        t->next = t->next->next;
        
        return head;
    }
};