Submission #206663

#	Time	Username	Problem	Language	Result	Execution time	Memory
206663		gratus907	두 로봇 (KOI18_robot)	C++17	0 / 100	186 ms	62860 KiB

robot

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define usecppio ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define all(x) ((x).begin()),((x).end())
#define eps 1e-7
#define int ll
using pii = pair <int, int>;
const int mod = 1000000007;
int n, a, b;
bool visited[101010];
int par[101010][21], maxedge[101010][21], minedge[101010][21];
int d[101010];
vector <pii> graph[101010]; // {destination, weight}
void dfs(int here,int depth) // run dfs(root,0)
{
    visited[here] = true;
    d[here] = depth;
    for (auto there : graph[here])
    {
        if (visited[there.first])
            continue;
        dfs(there.first, depth + 1);
        par[there.first][0] = here;
        maxedge[there.first][0] = there.second;
        minedge[there.first][0] = there.second;
    }
}

void precomputation()
{
    for (int i = 1; i<21; i++)
    {
        for (int j = 1; j<=n; j++)
        {
            par[j][i] = par[par[j][i-1]][i-1];
            maxedge[j][i] = max(maxedge[j][i - 1],
                                maxedge[par[j][i - 1]][i - 1]);
            minedge[j][i] = min(minedge[j][i - 1],
                                minedge[par[j][i - 1]][i - 1]);
        }
    }
}

pii lca(int x, int y)
{
    int maxlen = INT_MIN;
    int minlen = INT_MAX;
    if (d[x]>d[y])
        swap(x,y);
    for (int i = 20; i>=0; i--)
    {
        if (d[y]-d[x] >= (1<<i))
        {
            minlen = min(minlen,minedge[y][i]);
            maxlen = max(maxlen,maxedge[y][i]);
            y = par[y][i];
        }
    }
    if (x==y)
        return {par[x][0], maxlen};
    for (int i = 20; i>=0; i--)
    {
        if (par[x][i] != par[y][i])
        {
            minlen = min(minlen,min(minedge[x][i],minedge[y][i]));
            maxlen = max(maxlen,max(maxedge[x][i],maxedge[y][i]));
            x = par[x][i];
            y = par[y][i];
        }
    }
    minlen = min(minlen,min(minedge[x][0],minedge[y][0]));
    maxlen = max(maxlen,max(maxedge[x][0],maxedge[y][0]));

    int lca_point = par[x][0];
    return {lca_point, maxlen};
}

void tobedone()
{
    dfs(1,0);
    precomputation();
}
int dt[101010];
bool vst[101010];
int32_t main()
{
    usecppio
    cin >> n;
    cin >> a >> b;
    for (int i = 1; i<n; i++)
    {
        int u, v, w;
        cin >> u >> v >> w;
        graph[u].push_back({v,w});
        graph[v].push_back({u,w});
    }
    tobedone();
    queue <int> q;
    dt[1] = 0;
    vst[1] = true;
    q.push(1);
    while(!q.empty())
    {
        int x = q.front();
        q.pop();
        for (auto it:graph[x])
        {
            if (!vst[it.first])
            {
                q.push(it.first);
                dt[it.first] = dt[x]+it.second;
                vst[it.first] = true;
            }
        }
    }

    cout << dt[a] + dt[b] - 2*dt[lca(a, b).first]-lca(a, b).second;
}

• Subtask 1: 0 / 17
• Subtask 2: 0 / 19
• Subtask 3: 0 / 23
• Subtask 4: 0 / 41