Submission #968509

#	Time	Username	Problem	Language	Result	Execution time	Memory
968509		GrindMachine	Highway Tolls (IOI18_highway)	C++17	100 / 100	195 ms	13900 KiB

highway

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
using namespace __gnu_pbds;
 
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
 
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x, y) ((x + y - 1) / (y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
 
#define rep(i, n) for(int i = 0; i < n; ++i)
#define rep1(i, n) for(int i = 1; i <= n; ++i)
#define rev(i, s, e) for(int i = s; i >= e; --i)
#define trav(i, a) for(auto &i : a)
 
template<typename T>
void amin(T &a, T b) {
    a = min(a, b);
}
 
template<typename T>
void amax(T &a, T b) {
    a = max(a, b);
}
 
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
 
/*
 
refs:
http://www.algonotes.com/en/solutions-ioi2018/
edi
 
*/
 
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
 
#include "highway.h"
 
vector<pii> adj[N];
 
void find_pair(int n, std::vector<int> U, std::vector<int> V, int A, int B) {
    int m = sz(U);
    vector<pii> edges;
    rep(i,m){
        int u = U[i], v = V[i];
        edges.pb({u,v});
        adj[u].pb({v,i}), adj[v].pb({u,i});
    }
 
    // find an edge that lies on at least one sp from s to t
    ll all_light = -1;
 
    {
        vector<int> w(m);
        all_light = ask(w);
    }
 
    int lo = 0, hi = m-1;
    int first = -1;
 
    while(lo <= hi){
        int mid = (lo+hi) >> 1;
        vector<int> w(m);
        rep(i,mid+1){
            w[i] = 1;
        }
        auto res = ask(w);
 
        if(res != all_light){
            first = mid;
            hi = mid-1;
        }
        else{
            lo = mid+1;
        }
    }
        
    assert(first != -1);
 
    // split into 2 sets: closer to x and closer to y
    auto bfs = [&](int r){
        queue<int> q;
        vector<int> dis(n,-1);
        q.push(r);
        dis[r] = 0;

        while(!q.empty()){
            int u = q.front();
            q.pop();
 
            for(auto [v,id] : adj[u]){
                if(dis[v] != -1) conts;
                q.push(v);
                dis[v] = dis[u]+1;
            }
        }

        return dis;
    };
 
    auto [x,y] = edges[first];
    auto xy_edge = first;
    vector<int> node_type(n); // 0 = none, 1 = closer to x, 2 = closer to y
    auto disx = bfs(x);
    auto disy = bfs(y);
    rep(i,n){
        if(disx[i] < disy[i]) node_type[i] = 1;
        else if(disy[i] < disx[i]) node_type[i] = 2;
    }
 
    // bfs tree of x (ignore nodes with node_type[i] != 1)
    queue<int> q;
    vector<int> dis(n,-1);
    q.push(x);
    dis[x] = 0;
    vector<int> ordx;
 
    while(!q.empty()){
        int u = q.front();
        q.pop();
 
        for(auto [v,id] : adj[u]){
            if(dis[v] != -1) conts;
            if(node_type[v] != 1) conts;
            q.push(v);
            dis[v] = dis[u]+1;
            ordx.pb(id);
        }
    }
    
    // bfs tree of y (ignore nodes with node_type[i] != 2)
    fill(all(dis),-1);
    q.push(y);
    dis[y] = 0;
    vector<int> ordy;
 
    while(!q.empty()){
        int u = q.front();
        q.pop();
 
        for(auto [v,id] : adj[u]){
            if(dis[v] != -1) conts;
            if(node_type[v] != 2) conts;
            q.push(v);
            dis[v] = dis[u]+1;
            ordy.pb(id);
        }
    }

    // find s
    lo = 0, hi = sz(ordx);
    first = -1;
 
    while(lo <= hi){
        int mid = (lo+hi) >> 1;
        vector<int> w(m,1);
        
        w[xy_edge] = 0;
        trav(id,ordy){
            w[id] = 0;
        }
        rep(i,mid){
            w[ordx[i]] = 0;
        }
 
        auto res = ask(w);
 
        if(res == all_light){
            first = mid;
            hi = mid-1;
        }
        else{
            lo = mid+1;
        }
    }
 
    assert(first != -1);
    first--;
 
    int s = -1;
 
    if(first == -1){
        s = x;
    }
    else{
        auto [u,v] = edges[ordx[first]];
        if(disx[u] > disx[v]) s = u;
        else s = v;
    }
    
    // find t
    lo = 0, hi = sz(ordy);
    first = -1;
 
    while(lo <= hi){
        int mid = (lo+hi) >> 1;
        vector<int> w(m,1);
        
        w[xy_edge] = 0;
        trav(id,ordx){
            w[id] = 0;
        }
        rep(i,mid){
            w[ordy[i]] = 0;
        }
 
        auto res = ask(w);
 
        if(res == all_light){
            first = mid;
            hi = mid-1;
        }
        else{
            lo = mid+1;
        }
    }
 
    assert(first != -1);
    first--;
 
    int t = -1;
    
    if(first == -1){
        t = y;
    }
    else{
        auto [u,v] = edges[ordy[first]];
        if(disy[u] > disy[v]) t = u;
        else t = v;
    }

    answer(s,t);
}

• Subtask 1: 5 / 5
• Subtask 2: 7 / 7
• Subtask 3: 6 / 6
• Subtask 4: 33 / 33
• Subtask 5: 18 / 18
• Subtask 6: 31 / 31