HIHO #1069 : 最近公共祖先·三(RMQ+DFS LCA在线算法)

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<string>
#include<cmath>
#include<queue>
#include<map>
#include<set>
#include<cstdlib>
#include<vector>
using namespace std;
#define cl(a,b) memset(a,b,sizeof(a))
#define LL long long
#define pb push_back
#define gcd __gcd

#define For(i,j,k) for(int i=(j);i<k;i++)
#define lowbit(i) (i&(-i))
#define _(x) printf("%d\n",x)

const int maxn = 1e6+10;
const int inf  = 1 << 28;

int idd = 0;
map<string,int> mp;
map<int,string> tos;

int getid(string s){
if(!mp.count(s)){
mp[s]=idd;
tos[idd]=s;
return idd++;
}
return mp[s];
}

int dp[maxn][20];
int depth[maxn<<1];
int vis[maxn<<1];
int id[maxn];
vector<int> G[maxn];

void init_rmq(int n){
for(int i=0;i<n;i++)dp[i][0] = i;
for(int j=1;j<20;j++){
for(int i=0;i+(1<<j)-1<n;i++){
if(depth[dp[i][j-1]] < depth[dp[i+(1<<j-1)][j-1]])
dp[i][j]=dp[i][j-1];
else
dp[i][j]=dp[i+(1<<j-1)][j-1];
}
}
}

int query(int L,int R){
int k = log2(R-L+1);
if(depth[dp[L][k]]<depth[dp[R-(1<<k)+1][k]])
return dp[L][k];
return dp[R-(1<<k)+1][k];
}

void dfs(int u,int fa,int d,int &k){
vis[k] = u;
id[u] = k;
depth[k++] = d;
for(int i=0;i<G[u].size();i++){
int v = G[u][i];
if(v==u)continue;
dfs(v,u,d+1,k);
vis[k] = u;
depth[k++] = d;
}
}

int lca(int u,int v){
return vis[query(min(id[u],id[v]),max(id[u],id[v]))];
}

int root;
void solve(int n){
int k = 0;
dfs(root,-1,0,k);
init_rmq(n*2-1);
}

bool flag[maxn];
int main(){
int n;scanf("%d",&n);
for(int i=0;i<n;i++){
string a,b;cin>>a>>b;
G[getid(a)].pb(getid(b));
flag[getid(b)]=true;
}
for(int i=0;i<idd;i++)if(!flag[i]){root=i;break;}
solve(n);
int m;scanf("%d",&m);
while(m--){
string a,b;cin>>a>>b;
cout<<tos[lca(getid(a),getid(b))]<<endl;
}
return 0;
}