【景区导游——LCA】

题目

代码

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 1e5 + 10;
const int M = 2 * N;
int p[N][18], d[N], a[N];
ll dis[N][18]; //注意这里要开long long
int h[N], e[M], ne[M], idx, w[M];
int n, k;
void add(int a, int b, int c)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx, w[idx++] = c;
}
void dfs(int u)
{
    for (int i = h[u]; ~i; i = ne[i])
    {
        int j = e[i];
        if (d[j])
            continue;
        d[j] = d[u] + 1;
        p[j][0] = u;
        dis[j][0] = w[i];
        for (int k = 1; k <= 17; k++)
        {
            p[j][k] = p[p[j][k - 1]][k - 1];
            dis[j][k] = dis[j][k - 1] + dis[p[j][k - 1]][k - 1];
        }
        dfs(j);
    }
}
ll lca(int a, int b)
{
    ll retv = 0;

    if (d[a] < d[b])
        swap(a, b);
    for (int i = 17; i >= 0; i--)
    {
        if (d[p[a][i]] >= d[b])
        {
            retv += dis[a][i];
            a = p[a][i];
        }
    }

    if (a == b)
        return retv;

    for (int i = 17; i >= 0; i--)
    {
        if (p[a][i] != p[b][i])
        {
            retv += dis[a][i];
            retv += dis[b][i];
            a = p[a][i];
            b = p[b][i];
        }
    }

    retv += dis[a][0];
    retv += dis[b][0];

    return retv;
}
int main()
{
    memset(h, -1, sizeof h);

    cin >> n >> k;
    for (int i = 1; i < n; i++)
    {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
        add(b, a, c);
    }
    
    d[1] = 1;
    dfs(1);
    
    ll tmp = 0;
    cin >> a[1];
    for (int i = 2; i <= k; i++)
    {
        cin >> a[i];
        tmp += lca(a[i - 1], a[i]);
    }

    for (int i = 1; i <= k; i++)
    {
        ll ans = tmp;
        if (i == 1)
            ans -= lca(a[1], a[1 + 1]);
        else if (i == k)
            ans -= lca(a[k - 1], a[k]);
        else
        {
            ans -= lca(a[i - 1], a[i]);
            ans -= lca(a[i], a[i + 1]);
            ans += lca(a[i - 1], a[i + 1]);
        }

        cout << ans << ' ';
    }

    return 0;
}