Submission #556281

#	Time	Username	Problem	Language	Result	Execution time	Memory
556281		n0sk1ll	Race (IOI11_race)	C++17	0 / 100	3 ms	4948 KiB

race

#include "race.h"
#include <bits/stdc++.h>

#define xx first
#define yy second

using namespace std;
long long int typedef li;

vector<vector<pair<int,int>>> g(200005);
int ch[200005],ans=1e9;
bitset<200005> vis;

li K;

void dfs(int p, int q)
{
    ch[p]=1;
    for (auto [it,w] : g[p]) if (it!=q && !vis[it]) dfs(it,p),ch[p]+=ch[it];
}

int centroid(int p, int q, int s)
{
    int c=p;
    for (auto [it,w] : g[p]) if (it!=q && !vis[it])
    {
        int tmp=centroid(it,p,s);
        if (tmp!=-1) return tmp;
        if (2*ch[it]>s) c=-1;
    }
    if (2*ch[p]<s) c=-1;
    return c;
}

unordered_map<li,int> dub;

void add(int p, int q, li s, int d)
{
    auto it=dub.find(s);
    if (it==dub.end()) dub[s]=d;
    else it->yy=min(it->yy,d);
    for (auto [it,w] : g[p]) if (it!=q && !vis[it]) add(it,p,s+w,d+1);
}

void iter(int p, int q, li s, int d)
{
    auto it=dub.find(K-s);
    if (it!=dub.end()) ans=min(ans,d+it->yy);
    for (auto [it,w] : g[p]) if (it!=q && !vis[it]) iter(it,p,s+w,d+1);
}

void decomp(int p)
{
    dfs(p,-1);
    int c=centroid(p,-1,ch[p]);
    //cout<<","<<c<<endl;

    dub.clear(); dub[0]=0;
    for (auto [it,w] : g[c]) if (!vis[it]) iter(it,p,w,1),add(it,p,w,1);

    vis[c]=1;
    for (auto [it,w] : g[c]) if (!vis[it]) decomp(it);
}

int best_path(int n, int k, int H[][2], int L[])
{
    for (int i=0;i<n-1;i++) g[H[i][0]].push_back({H[i][1],L[i]}),g[H[i][1]].push_back({H[i][0],L[i]});
    K=k,decomp(0); return (ans==1e9?-1:ans);
}

/*

11 12
0 1 3
0 2 4
2 3 5
3 4 4
4 5 6
0 6 3
6 7 2
6 8 5
8 9 6
8 10 7

7 3
0 1 1
0 4 1
4 5 1
5 6 1
1 2 3
1 3 2

7 8
0 1 1
0 4 1
4 5 1
5 6 1
1 2 3
1 3 2

*/

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