hihoCoder#1067 最近公共祖先·二

 1 #include <iostream>
 2 #include <map>
 3 #include <set>
 4 #include <vector>
 5 #include <cstring>
 6 
 7 using namespace std;
 8 
 9 #define SIZE 100010
10 
11 int N, M;
12 vector<int> tree[SIZE];
13 int color[SIZE];
14 int ancestor[SIZE];
15 vector<pair<int, int> > query[SIZE];
16 int ans[SIZE];
17 map<string, int> a2i;
18 string i2a[SIZE];
19 
20 int find_gray(int node) {
21   if (color[node] == 1)
22     return node;
23   int gray = find_gray(ancestor[node]);
24   ancestor[node] = gray;
25   return gray;
26 }
27 
28 void traverse(int root) {
29   color[root] = 1;
30   for (auto q : query[root]) {
31     if (ans[q.second] != 0)
32       continue;
33     if (color[q.first] == 1)
34       ans[q.second] = q.first;
35     if (color[q.first] == 2)
36       ans[q.second] = find_gray(q.first);
37   }
38 
39   for (auto c : tree[root])
40     traverse(c);
41 
42   color[root] = 2;
43 }
44 
45 int main() {
46   memset(color, 0, SIZE * sizeof(int));
47   memset(ancestor, 0, SIZE * sizeof(int));
48   memset(ans, 0, SIZE * sizeof(int));
49 
50   int order = 1;
51   cin >> N;
52   for (int i = 0; i < N; i++) {
53     string f, s;
54     int fi, si;
55     cin >> f >> s;
56     fi = a2i[f];
57     si = a2i[s];
58     if (fi == 0) {
59       fi = a2i[f] = order;
60       i2a[order] = f;
61       order++;
62     }
63     if (si == 0) {
64       si = a2i[s] = order;
65       i2a[order] = s;
66       order++;
67     }
68     tree[fi].push_back(si);
69     ancestor[si] = fi;
70     color[fi] = color[si] = 0;
71   }
72   cin >> M;
73   for (int i = 0; i < M; i++) {
74     string a, b;
75     int ai, bi;
76     cin >> a >> b;
77     ai = a2i[a];
78     bi = a2i[b];
79     query[ai].push_back(pair<int, int>(bi, i));
80     query[bi].push_back(pair<int, int>(ai, i));
81   }
82 
83   traverse(1);
84 
85   for (int i = 0; i < M; i++)
86     cout << i2a[ans[i]] << endl;
87 
88   return 0;
89 }