hihoCoder week17 最近公共祖先·三 lca st表

#include <bits/stdc++.h>
using namespace std;

const int N = 2e5+10;

int n, cnt, tot, dp[N][21]; // dp[i][j] [i, i+(1<<j)-1]
vector<int> G[N]; map<string ,int> mp;
string s1,s2,s[N];

int dfn[N], id[N], dep[N];
int getId(string str)
{
    if(mp[str]) 
        return mp[str];
    mp[str] = ++cnt;
    s[cnt] = str;
    return cnt;
}

void dfs(int u,int fa,int d)
{
    id[u] = tot;
    dfn[tot] = u;
    dep[tot++] = d;
    
    for(int i=0; i<G[u].size(); i++) {
        int v = G[u][i];
        dfs(v, u, d+1);
        dfn[tot] = u;
        dep[tot++] = d;
    }
    return ;
}

void st_init(int sz)
{
    for(int i=1; i<=sz; i++) 
        dp[i][0] = i;
    for(int j=1; (1<<j)<=sz; j++)
    {
        for(int i=1; i+(1<<j)-1<=sz; i++)
        {
            int x = dp[i][j-1];
            int y = dp[i+(1<<(j-1))][j-1];
            if(dep[x] < dep[y])
                dp[i][j] = x;
            else 
                dp[i][j] = y;
        }
    }
}

void init()
{
    tot = 1;
    dfs(1, 0, 0);
    st_init(tot-1);
}

int query(int u,int v)
{
    u = id[u], v = id[v];
    if(v < u)
        swap(v,u);
    int t = log2(v-u+1);
    int x = dp[u][t];
    int y = dp[v-(1<<t)+1][t];
    if(dep[x] < dep[y])
        return x;
    else 
        return y;
}
int main()
{
    freopen("in.txt","r",stdin);
    ios::sync_with_stdio(0);
    cin >> n;
    for(int i=0; i<n; i++) {
        cin >> s1 >> s2;
        int u = getId(s1);
        int v = getId(s2);
        G[u].push_back(v);
    }
    init();
    int m; cin >> m;
    for(int i=0; i<m; i++) {
        cin >> s1 >> s2;
        int u = getId(s1);
        int v = getId(s2);
        int x = dfn[query(u,v)];
        cout << s[x] <<"\n";
    }
    return 0;
}