Submission #604661

#	Time	Username	Problem	Language	Result	Execution time	Memory
604661		PiejanVDC	Highway Tolls (IOI18_highway)	C++17	18 / 100	401 ms	46436 KiB

highway

#include "highway.h"
#include <bits/stdc++.h>
using namespace std;
 
const int mxN = (int)9e4+5;
 
int def;
long long normal;
int N_;
 mt19937 mt(time(nullptr)); 
long long ask(const std::vector<int> &w);
void answer(int s, int t);
 
map<pair<int,int>, int>id;
vector<int>re(mxN);
 
int search_point(vector<int>points) {
    int n = (int)points.size();
    int ans = -1;
 
    int l = 0, r = n-1;
    while(l < r) {
        int mid = (l+r)/2;
        vector<int>Ask(N_, 0);
        for(int i = l ; i <= mid ; i++)
            Ask[points[i]] = 1;
        if(ask(Ask) != normal) {
            r = mid;
            ans = mid;
        } else l = mid+1;
    }
    return points[r];
}
 
bool present(vector<int>points) { 
    vector<int>Ask(N_, 0);
    for(auto z : points)
        Ask[z] = 1;
    return ask(Ask) != normal;
}
 
vector<int>p[mxN];
vector<int>parent(mxN);
 
vector<int>adj[mxN];
 
int mxDist;
 
int A_ = -2;
int h = -2;
 
void dfs(int node, int dist, int e = -1) {
    if(node == h) return;
    mxDist = max(mxDist, dist);
    if(e > -1) p[dist].push_back(id[{node, e}]);
    parent[node] = e;
    re[node] = dist;
    for(auto z : adj[node]) if(z != e) dfs(z, dist+1, node);
}
 
int distance() {
    int l = 1, r = mxDist-1;
    int ans = -1;
    while(l <= r) {
        int mid = (l+r)/2;
        if(present(p[mid]))
            ans = mid, l = mid+1;
        else
            r = mid-1;
    }
    return ans;
}
 
void delete_(int a) {
    if(a == def) return;
    for(int i = 0 ; i <= mxDist ; i++)
        p[i].clear();
    stack<int>s;
    s.push(a);
    vector<bool>vis(N_+1, 0);
    vis[a] = 1;
    while(1) {
        int node = s.top();
        s.pop();
        for(auto z : adj[node]) if(!vis[z]) {
            if(z == def) {
                h = node;
                return;
            }
            vis[z] = 1;
            s.push(z);
        }
    } 
}
    
void find_pair(int n, vector<int>u, vector<int>v, int a_, int b_) {
    N_ = n-1;
 
    vector<int>dummy(n-1, 0);
    normal = ask(dummy);
 
    vector<int>rev(n-1);
    for(int i = 0 ; i < n-1 ; i++)
        id[{u[i], v[i]}] = id[{v[i], u[i]}] = i, rev[i] = u[i], adj[u[i]].push_back(v[i]), adj[v[i]].push_back(u[i]);
 
    vector<int>d(n-1);
    for(int i = 0 ; i < n-1 ; i++)
        d[i] = i;
    def = rev[search_point(d)];
    dfs(def, 0);
 
    int a = distance();
    if(a == -1)
        A_ = def;
    else {
        A_ = search_point(p[a]);
        A_ = (re[u[A_]] > re[v[A_]] ? u[A_] : v[A_]);   
    }
    
    delete_(A_);
    mxDist = 0;
    dfs(def, 0);
 
    long long need = normal / a_ - max(0, a);
 
    int b = need;
    int B_ = -1;
    if(b == 0)
        B_ = def;
    else {
        B_ = search_point(p[b]);
        B_ = (re[u[B_]] > re[v[B_]] ? u[B_] : v[B_]);
    }
    answer(A_, B_);
}

Compilation message (stderr)

highway.cpp: In function 'int search_point(std::vector<int>)':
highway.cpp:19:9: warning: variable 'ans' set but not used [-Wunused-but-set-variable]
   19 |     int ans = -1;
      |         ^~~

• Subtask 1: 5 / 5
• Subtask 2: 7 / 7
• Subtask 3: 6 / 6
• Subtask 4: 0 / 33
• Subtask 5: 0 / 18
• Subtask 6: 0 / 31