C + + algorithm in the list of the penultimate K nodes

Title: Enter a list, output the list of the countdown K nodes, in order to conform to the majority of the habit, the topic from 1 to count, that is, the tail node of the list is the penultimate node.

Method 1: The list is traversed first to get the number of the list n, the penultimate K node is n-k+1 and then traverse the list, find the N-k+1 node is the penultimate K node; This method traverses two linked lists;

Method 2: First traverse the list to press the linked list into a stack, then out of the stack, the K-time out of the stack is the K-node;

Method 3: First reverse the linked list, then traverse

Method 4: Define two pointers, the first pointer starts from the head pointer of the list to traverse forward k-1; the second pointer remains motionless, starting with step K, the second pointer also begins to traverse, two pointer gaps k-1 distance

, when the first pointer goes to the tail node, the second pointer is exactly at the bottom of the K-node;

Code:

listnode* Findkthfromtail (listnode* plisthead,int k) {if (Plisthead = NULL | | k = = 0)//Prevent empty linked list  and K value equals 0 case {return NUL L;} listnode* pahead = Plisthead; listnode* pbehind = null;for (int i = 0; i < k-1; i++) {if (Pahead->m_pnext! = NULL) {pahead = Pahead->m_pnext;} Else{return NULL;}} Pbehind = Plisthead;while (pahead->m_pnext! = NULL) {Pahead  = Pahead->m_pnext;pbehind = Pbehind->m_pnext;} return pbehind;}

All complete code:

FindKthFromTail.cpp: Defines the entry point of the console application. #include "stdafx.h" #include <iostream>using namespace std;struct listnode {int m_nvalue; listnode* M_pnext; ListNode (int k): M_nvalue (k), M_pnext (NULL) {}}; listnode* Findkthfromtail (listnode* plisthead,int k) {if (Plisthead = = NULL | | k = = 0)//Prevent empty linked list and K value equal to 0 case {return NULL;} listnode* pahead = Plisthead; listnode* pbehind = null;for (int i = 0; i < k-1; i++) {if (Pahead->m_pnext! = NULL) {pahead = Pahead->m_pnext;} Else{return NULL;}} Pbehind = Plisthead;while (pahead->m_pnext! = NULL) {pahead = Pahead->m_pnext;pbehind = Pbehind->m_pnext;} return pbehind;} int _tmain (int argc, _tchar* argv[]) {listnode* head = new ListNode (1); listnode* Node1 = new ListNode (2); listnode* Node2 = new ListNode (3); listnode* Node3 = new ListNode (4); listnode* Node4 = new ListNode (5); listnode* NODE5 = new ListNode (6); listnode* Node6 = new ListNode (7); head->m_pnext = Node1; Node1->m_pnext = Node2; Node2->m_pnext = Node3; Node3->m_pnext = Node4; Node4->m_pnext = NODE5; Node5->m_pnext = Node6; Node6->m_pnext = NULL; listnode* p = findkthfromtail (head,3); Cout<<p->m_nvalue<<endl;getchar (); return 0;}

C + + algorithm in the list of the penultimate K nodes