Submission #876336

#	Time	Username	Problem	Language	Result	Execution time	Memory
876336		MON	Race (IOI11_race)	C++14	100 / 100	1038 ms	80244 KiB

race

#include "race.h"
#include<vector>
#include<unordered_map>
#include<bitset>
#include<algorithm>
#define fi first
#define se second
using namespace std;
using pii = pair<int,int>;
using ll = long long;

constexpr int NMAX = 2e5 + 1;
vector<pii> fii[NMAX]; bitset<NMAX> scos;
int sz[NMAX],n,k,mx,ans;

void build(int r,int p = -1)
{
    sz[r] = 1;
    for(auto &it : fii[r])
        if(it.first != p && !scos[it.first])
            build(it.first,r),sz[r] += sz[it.first];
}

int centroid(int r,int n,int p = -1)
{
    for(auto &it : fii[r])
        if(it.first != p && !scos[it.first] && sz[it.first] * 2 > n)
            return centroid(it.first,n,r);
    return r;
}

void dfs(int a,ll cost,int d,int p,bool add,unordered_map<int,int> &m,unordered_map<int,bool> &avem)
{
    if(cost > k) return;
    if(add)
        {
            bool &u = avem[cost];
            if(!u) u = 1 , m[cost] = d;
            else
                {
                    int &h = m[cost];
                    h = min(h,d);
                }
        }

    else
        {
            bool &u = avem[k-cost];
            if(u) ans = min(ans,m[k-cost]+d);
        }

    for(auto &it : fii[a])
        if(!scos[it.fi] && it.fi != p) dfs(it.fi,cost+it.se,d+1,a,add,m,avem);
    mx = max(mx,d);
}

void descompune(int root)
{
    build(root); int c = centroid(root,sz[root]);
    unordered_map<int,int> nou; unordered_map<int,bool> avem; avem[0] = 1;
    for(auto &it : fii[c])
        if(!scos[it.fi])
            dfs(it.fi,it.se,1,c,0,nou,avem),
            dfs(it.fi,it.se,1,c,1,nou,avem);

    mx = 0; scos[c] = 1;
    for(auto &it : fii[c])
        if(!scos[it.fi]) descompune(it.fi);
}

int best_path(int N,int K,int H[][2],int L[])
{
    n = N,k = K; ans = n + 1;
    for(int i = 0 ; i < n - 1; i ++)
        {
            fii[H[i][0]].push_back({H[i][1],L[i]});
            fii[H[i][1]].push_back({H[i][0],L[i]});
        }

    descompune(0); if(ans == n + 1) ans = -1;
    return ans;
}

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