九度 链表中倒数第k个结点

/*
 * a.cpp
 *
 *  Created on: 2013-10-7
 *      Author: wangzhu
 */

#include<cstdio>
#include<iostream>
using namespace std;
struct Node {
    int key;
    Node* next;
};

void addToHead(Node* root, int val) {
    Node* tempNode = root->next;

    Node* node = new Node;
    node->key = val;
    node->next = tempNode;

    root->next = node;
}

void addToTail(Node* root, int val) {
    Node* node = new Node;
    node->key = val;
    node->next = NULL;
    if (root->next == NULL) {
        root->next = node;
    } else {
        Node* tempNode = root->next;
        while (tempNode->next != NULL) {
            tempNode = tempNode->next;
        }
        tempNode->next = node;
    }
}

void printHead(Node* node, int k) {
    for (int i = 1; i < k; i++) {
        node = node->next;
    }
    printf("%d\n", node->key);
}

void printTail(Node* node, int k) {
    Node* firstNode = node;
    Node* secondNode = node;
    for (int i = 1; i < k; i++) {
        firstNode = firstNode->next;
    }
    while (firstNode->next != NULL) {
        firstNode = firstNode->next;
        secondNode = secondNode->next;
    }
    printf("%d\n", secondNode->key);
}
int main() {
    freopen("data.in", "r", stdin);
    Node* root;
    int n, k, val;
    while (~scanf("%d%d", &n, &k)) {
        root = new Node;
        root->next = NULL;
        for (int i = 0; i < n; i++) {
            scanf("%d", &val);
            //addToHead(root, val);
            addToTail(root,val);
        }
        if (n == 0 || k == 0 || n < k) {
            printf("NULL\n");
        } else {
            //printHead(root->next, k);
            printTail(root->next,k);
        }
    }
    return 0;
}