PAT 1032. Sharing

其实就是链表求交：

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

 using namespace std;

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

 void print_list(unordered_map<int, Node*>& mem, int head) {
     int cur = head;
     while (cur != -) {
         cout<<mem[cur]->data<<" ";
         cur = mem[cur]->next;
     }
     cout<<endl;
 };

 int step_list(unordered_map<int, Node*>& mem, int from, int n) {
     if (n < ) return -;
     int cur = from;
     while (cur != -) {
         if (n == ) {
             break;
         }
         cur = mem[cur]->next;
         n--;
     }
     return cur;
 }

 int count_list(unordered_map<int, Node*>& mem, int from) {
     if (from < ) return ;
     int cur =  from;
     int cnt = ;
     while (cur != -) {
         cur = mem[cur]->next;
         cnt++;
     }
     return cnt;
 }

 int main() {
     int head_a, head_b;
     int n;

     unordered_map<int, Node*> mem;

     cin>>head_a>>head_b>>n;

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

     int cnt_a = count_list(mem, head_a);
     int cnt_b = count_list(mem, head_b);

     int cnt_diff = cnt_a - cnt_b;
     int head_long  = head_a;
     int head_short = head_b;
     if (cnt_diff < ) {
         cnt_diff = -cnt_diff;
         head_long = head_b;
         head_short= head_a;
     }

     head_long = step_list(mem, head_long, cnt_diff);

     while (head_long != head_short) {
         head_long = mem[head_long]->next;
         head_short= mem[head_short]->next;
     }
     if (head_long < ) {
         printf("-1\n");
     } else {
         printf("%05d\n", head_long);
     }
     system("pause");
     return ;
 }