Submission #217363

#	Time	Username	Problem	Language	Result	Execution time	Memory
217363		Autoratch	Race (IOI11_race)	C++17	0 / 100	18 ms	16048 KiB

race

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

const int N = 2e5 + 1;
const int K = 20;

vector<pair<int,int> > adj[N];
int sz[N],pa[N],lv[N],dp[K][N],ans = INT_MAX;
bool blocked[N];
long long dist[N];
unordered_map<int,int> res[N];

void dfs(int u,int p){ sz[u] = 1; for(auto [d,v] : adj[u]) if(v!=p and !blocked[v]) dfs(v,u),sz[u]+=sz[v]; }

void build(int u,int cp)
{
    dfs(u,0);
    int c = u,prev = 0;
    while(true)
    {
        int mx = 0,id = 0;
        for(auto [d,v] : adj[c]) if(!blocked[v] and v!=prev) if(sz[v]>mx) mx = sz[v],id = v;
        if(mx*2>sz[u]) prev = c,c = id;
        else break;
    }
    pa[c] = cp;
    blocked[c] = true;
    for(auto [d,v] : adj[c]) if(!blocked[v]) build(v,c);
}

void dfslca(int u,int p){ lv[u] = lv[p]+1,dp[0][u] = p; for(auto [d,v] : adj[u]) if(v!=p) dist[v] = dist[u]+(long long)d,dfslca(v,u); }

int lca(int a,int b)
{
    if(lv[a]<lv[b]) swap(a,b);
    for(int i = K-1;i >= 0;i--) if(lv[dp[i][a]]>=lv[b]) a = dp[i][a];
    if(a==b) return a;
    for(int i = K-1;i >= 0;i--) if(dp[i][a]!=dp[i][b]) a = dp[i][a],b = dp[i][b];
    return dp[0][a];
}

int best_path(int n,int k,int h[][2],int l[])
{
    for(int i = 0;i < n-1;i++)
    {
        int a = h[i][0],b = h[i][1],d = l[i]; a++,b++;
        adj[a].push_back({d,b});
        adj[b].push_back({d,a});
    }
    build(1,0);
    dfslca(1,0);
    for(int i = 1;i <= n;i++)
    {
        for(int u = pa[i];u;u = pa[u])
        {
            int l = lca(i,u);
            long long all = dist[i]-dist[l]+dist[u]-dist[l];
            if(all>k) continue;
            int len = lv[i]-lv[l]+lv[u]-lv[l];
            if(res[u][all]==0 or res[u][all]>len)
            {
                res[u][all] = len;
                if(all==k) ans = min(ans,len);
                else if(res[u][k-all]) ans = min(ans,res[u][k-all]+len);
            }
        }
    }
    if(ans==INT_MAX) ans = -1;
    return ans;
}

Compilation message (stderr)

race.cpp: In function 'void dfs(int, int)':
race.cpp:14:48: warning: unused variable 'd' [-Wunused-variable]
 void dfs(int u,int p){ sz[u] = 1; for(auto [d,v] : adj[u]) if(v!=p and !blocked[v]) dfs(v,u),sz[u]+=sz[v]; }
                                                ^
race.cpp: In function 'void build(int, int)':
race.cpp:23:22: warning: unused variable 'd' [-Wunused-variable]
         for(auto [d,v] : adj[c]) if(!blocked[v] and v!=prev) if(sz[v]>mx) mx = sz[v],id = v;
                      ^
race.cpp:29:18: warning: unused variable 'd' [-Wunused-variable]
     for(auto [d,v] : adj[c]) if(!blocked[v]) build(v,c);
                  ^

• Subtask 1: 0 / 9
• Subtask 2: 0 / 12
• Subtask 3: 0 / 22
• Subtask 4: 0 / 57