hihoCoder #1067 : 最近公共祖先·二 [ 离线LCA tarjan ]

  1 #include <cstdio>
  2 #include <cstring>
  3 #include <iostream>
  4 #include <algorithm>
  5 #include <stack>
  6 #include <cctype>
  7 #include <vector>
  8 #include <cmath>
  9 #include <map>
 10 
 11 #define ll long long
 12 
 13 using namespace std;
 14 
 15 const int N = 100005;
 16 const int M = 105;
 17 const ll mod = 1000000007;
 18 
 19 int n,m;
 20 int tot;
 21 map<string,int> mp;
 22 int f[N];
 23 char s1[N],s2[N];
 24 vector<int> G[N];
 25 int vis[N];
 26 
 27 struct PP
 28 {
 29     int next;
 30     int index;
 31     PP(int tn,int ti)
 32     {
 33         next = tn;
 34         index = ti;
 35     }
 36 };
 37 
 38 vector<PP> query[N];
 39 
 40 string name[N];
 41 string ans[N];
 42 
 43 int find(int x)
 44 {
 45     return f[x] == x ? f[x] : f[x] = find(f[x]);
 46 }
 47 
 48 void merge(int x,int y)
 49 {
 50     int a=find(x);
 51     int b=find(y);
 52     if(a==b) return;
 53     f[b]=a;
 54 }
 55 
 56 void ini()
 57 {
 58     tot=0;
 59     int i;
 60     int x,y;
 61     for(i=0;i<=n;i++){
 62         G[i].clear();
 63         query[i].clear();
 64         f[i]=i;
 65     }
 66     for(i=1;i<=n;i++){
 67         scanf("%s%s",s1,s2);
 68         if(mp.count(s1)==0){
 69             tot++;
 70             mp[s1]=tot;
 71             x=tot;
 72             name[tot]=s1;
 73         }
 74         else{
 75             x=mp[s1];
 76         }
 77         if(mp.count(s2)==0){
 78             tot++;
 79             mp[s2]=tot;
 80             y=tot;
 81             name[tot]=s2;
 82         }
 83         else{
 84             y=mp[s2];
 85         }
 86 
 87         G[x].push_back(y);
 88         G[y].push_back(x);
 89     }
 90 
 91     scanf("%d",&m);
 92     for(i=1;i<=m;i++){
 93         scanf("%s%s",s1,s2);
 94         x=mp[s1];
 95         y=mp[s2];
 96         query[x].push_back(PP(y,i));
 97         query[y].push_back(PP(x,i));
 98     }
 99 }
100 
101 void tarjan(int u,int fa)
102 {
103     int i;
104     int v;
105     //printf(" u=%d fa=%d\n",u,fa);
106     for(i=0;i<G[u].size();i++){
107         v=G[u][i];
108         if(v==fa) continue;
109         tarjan(v,u);
110     }
111     int index;
112     vis[u]=1;
113 
114     for(i=0;i<query[u].size();i++){
115         v=query[u][i].next;
116         index=query[u][i].index;
117        // printf("  i=%d v=%d index=%d\n",i,v,index);
118         if(vis[v]==0) continue;
119         ans[index]=name[find(v)];
120     }
121     f[u]=fa;
122 }
123 
124 void solve()
125 {
126     memset(vis,0,sizeof(vis));
127     tarjan(1,-1);
128 }
129 
130 void out()
131 {
132     int i;
133     for(i=1;i<=m;i++){
134         cout<<ans[i]<<endl;
135     }
136 }
137 
138 int main()
139 {
140     //freopen("data.in","r",stdin);
141     //scanf("%d",&T);
142     //for(int ccnt=1;ccnt<=T;ccnt++){
143     while(scanf("%d",&n) != EOF) {
144         ini();
145         solve();
146         out();
147     }
148     return 0;
149 }