PAT 1074. Reversing Linked List

 #include <cstdio>
 #include <cstdlib>
 #include <iostream>
 #include <unordered_map>

 using namespace std;

 class Node {
 public:
     int data;
     int next;
     Node() : data(), next() {}
     Node(int d, int n):data(d), next(n){}
 };

 int reverse_help(int head, int k, unordered_map<int, Node>& mem) {
     if (head == -) {
         return -;
     }

     int cur = head;
     int prev= -;
     while (cur != -) {
         if (k == ) {
              break;
         }
         int tmp = mem[cur].next;
         mem[cur].next = prev;
         prev = cur;
         cur = tmp;

         k--;
     }
     mem[head].next = cur;
     return prev;
 }

 int reverse(int head, int k, unordered_map<int, Node>& mem, int n) {
     if (head == -) {
         return -;
     }

     int nhead = -;
     int cur = head;
     int pre = -; 

     while (cur != -) {
         int t = reverse_help(cur, k, mem);
         if (nhead == -) {
             nhead = t;
         }
         if (pre != -) {
             mem[pre].next = t;
         }
         pre = cur;
         cur = mem[cur].next;
         n -= k;
         if (n < k) {
             break;
         }
     }

     return nhead;
 }

 void print(int head, unordered_map<int, Node>& mem) {
     int cur = head;
     while(cur != -) {
         Node& cnode = mem[cur];
         if (cnode.next != -) {
             printf("%05d %d %05d\n", cur, cnode.data, cnode.next);
         } else {
             printf("%05d %d %d\n", cur, cnode.data, cnode.next);
         }
         cur = mem[cur].next;
     }
 }

 int count(int head, unordered_map<int, Node>& mem) {
     int cnt = ;
     int cur = head;
     while(cur != -) {
         cnt++;
         cur = mem[cur].next;
     }
     return cnt;
 }

 int main() {

     int head, n, k;
     scanf("%d%d%d", &head, &n, &k);

     unordered_map<int, Node> mem;

     for (int i=; i<n; i++) {
         int addr, data, next;
         scanf("%d%d%d", &addr, &data, &next);
         mem.insert(make_pair(addr, Node(data, next)));
     }

     cout<<"===="<<endl;
     print(head, mem);
     cout<<"===="<<endl;
     head = reverse(head, k, mem, count(head, mem));
     print(head, mem);

     return ;
 }

卧槽，敢再无聊点么，输入节点数据竟然有不含在链表里的节点数据。