PAT 1032. Sharing

其实就是链表求交：

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstdlib>
 4 #include <unordered_map>
 5
 6 using namespace std;
 7
 8 class Node {
 9 public:
10     Node() : data(0), next(0) {}
11     char data;
12     int next;
13 };
14
15 void print_list(unordered_map<int, Node*>& mem, int head) {
16     int cur = head;
17     while (cur != -1) {
18         cout<<mem[cur]->data<<" ";
19         cur = mem[cur]->next;
20     }
21     cout<<endl;
22 };
23
24 int step_list(unordered_map<int, Node*>& mem, int from, int n) {
25     if (n < 0) return -1;
26     int cur = from;
27     while (cur != -1) {
28         if (n == 0) {
29             break;
30         }
31         cur = mem[cur]->next;
32         n--;
33     }
34     return cur;
35 }
36
37 int count_list(unordered_map<int, Node*>& mem, int from) {
38     if (from < 0) return 0;
39     int cur =  from;
40     int cnt = 0;
41     while (cur != -1) {
42         cur = mem[cur]->next;
43         cnt++;
44     }
45     return cnt;
46 }
47
48 int main() {
49     int head_a, head_b;
50     int n;
51
52     unordered_map<int, Node*> mem;
53
54     cin>>head_a>>head_b>>n;
55
56     for (int i=0; i<n; i++) {
57         int addr;
58         Node* np = new Node();
59         scanf("%d %c %d", &addr, &(np->data), &(np->next));
60         mem.insert(make_pair(addr, np));
61     }
62
63     int cnt_a = count_list(mem, head_a);
64     int cnt_b = count_list(mem, head_b);
65
66     int cnt_diff = cnt_a - cnt_b;
67     int head_long  = head_a;
68     int head_short = head_b;
69     if (cnt_diff < 0) {
70         cnt_diff = -cnt_diff;
71         head_long = head_b;
72         head_short= head_a;
73     }
74
75     head_long = step_list(mem, head_long, cnt_diff);
76
77     while (head_long != head_short) {
78         head_long = mem[head_long]->next;
79         head_short= mem[head_short]->next;
80     }
81     if (head_long < 0) {
82         printf("-1\n");
83     } else {
84         printf("%05d\n", head_long);
85     }
86     system("pause");
87     return 0;
88 }