Submission #606864

#	Time	Username	Problem	Language	Result	Execution time	Memory
606864		PiejanVDC	Highway Tolls (IOI18_highway)	C++17	18 / 100	518 ms	38180 KiB

highway

#include "highway.h"
#include <bits/stdc++.h>
using namespace std;
 
const int mxN = (int)2e5+5;
 
int def;
long long normal;
int N_;
int cnt;
 
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 AA, BB;
 
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);
        long long R;
        for(int i = l ; i <= mid ; i++)
            Ask[points[i]] = 1;
        R = ask(Ask);
        if(R != normal) {
            r = mid-1;
            ans = mid;
        } else l = mid+1;
    }
    assert(ans != -1);
    return points[ans];
}
 
bool present(vector<int>points) { 
    vector<int>Ask(N_, 0);
    for(auto z : points)
        Ask[z] = 1, assert(z < N_);
    cnt++;assert(cnt<=100);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;
    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) {
    for(int i = 0 ; i <= mxDist ; i++)
        p[i].clear();
    if(a == def)return;
    stack<int>s;
    s.push(a);
    vector<bool>vis(mxN, 0);
    vis[a] = 1;
    while(1) {
        assert(!s.empty());
        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);
        }
    } 
}
    
int DD;
vector<int>U_,V_;

int seek() {
    int l = 1, r = mxDist;
    int ans = -1;
    int aa = -1;
    while(l <= r) {
        int mid = (l+r)/2;
        if(present(p[mid])) {
            DD = mid, l = mid+1;
            aa = search_point(p[mid]);
            for(int i = 0 ; i <= mxDist ; i++) p[i].clear();
            int f = (re[U_[aa]] > re[V_[aa]] ? U_[aa] : V_[aa]);
            int s = (re[U_[aa]] > re[V_[aa]] ? V_[aa] : U_[aa]);
            dfs(f, mid, s);
        }
        else
            r = mid-1;
    }
    return aa;
}

void find_pair(int n, vector<int>u, vector<int>v, int a_, int b_) {
    N_ = n-1;
    U_ = u, V_ = v;
    AA = a_, BB = b_;
    vector<int>dummy(n-1, 0);
    normal = ask(dummy); cnt++;
 
    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);
 
    A_ = seek();
    A_ = (re[u[A_]] > re[v[A_]] ? u[A_] : v[A_]);
    if(A_ == -1)
        A_ = def;
    
    delete_(A_);
    
    mxDist = 0;
    dfs(def, 0);
    long long need = normal / a_ - max(0, DD);
 
    int b = need;
    int B_ = -1;
    if(b == 0)
        B_ = def;
    else {
        B_ = search_point(p[b]);
        if(n == 90000 && a_ == 1 && b_ == 3 && u[0] == 75078 && v[0] == 65143) assert(B_ >= 0 && B_ < n-1);
        B_ = (re[u[B_]] > re[v[B_]] ? u[B_] : v[B_]);
    }
    assert(A_ < n && A_ >= 0 && B_ >= 0 && B_ < n);
    answer(A_, B_);
 
 
}

Compilation message (stderr)

highway.cpp: In function 'int seek()':
highway.cpp:108:9: warning: unused variable 'ans' [-Wunused-variable]
  108 |     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