hiho15周离线lca

它上面讲的很详细。

http://hihocoder.com/problemset/problem/1067?sid=210395

#include<iostream>
#include<cstdio>
#include<cstring>
#include<map>
#include<vector>
using namespace std;
const int maxn = 111111;

int father[maxn];
struct Node
{
    int next; int to;
}e[maxn * 2];
int len;
int head[maxn];
int color[maxn];
int l[maxn]; int r[maxn];
map<pair<int, int>, int> ans;
vector<int> q[maxn];
int getfather(int x)
{
    if (x != father[x]) father[x] = getfather(father[x]);
    return father[x];
}

void un(int a, int b)
{
    int fa = getfather(a); int fb = getfather(b);
    father[fb] = fa;
}

void add(int from, int to)
{
    e[len].to = to;
    e[len].next = head[from];
    head[from] = len++;
}

void dfs(int x)
{
    for (int i = head[x]; i != -1; i = e[i].next){
        int cc = e[i].to;
        dfs(cc);
        un(x, cc);
    }
    color[x] = 1;
    for (int i = 0; i < q[x].size(); i++){
        int t = q[x][i];
        if (color[t]){
            ans[make_pair(x, t)] = getfather(t);
            ans[make_pair(t, x)] = getfather(t);
        }
    }
}

int main()
{
    string a, b;

    int n;
    map<string, int> m;
    map<int, string> m1;
    cin >> n;
    int k;
    int sum = 1;
    len = 0;
    memset(head, -1, sizeof(head));
    for (int i = 0; i < n; i++){
        cin >> a >> b; int c; int d;
        if (!m.count(a)) m[a] = sum, m1[sum] = a, sum++;
        if (!m.count(b)) m[b] = sum, m1[sum] = b, sum++;
        c = m[a]; d = m[b];
        add(c, d);
    }
    for (int i = 0; i<maxn; i++) father[i] = i;
    cin >> k;
    for (int i = 0; i < k; i++){
        cin >> a >> b;
        int c = m[a]; int d = m[b];
        l[i] = c; r[i] = d;
        q[c].push_back(d);
        q[d].push_back(c);
    }
    memset(color, 0, sizeof(color));
    dfs(1);
    for (int i = 0; i < k; i++){
        cout<<m1[ans[make_pair(l[i],r[i])]]<<endl;
    }
    return 0;
}