Submission #611768

#	Time	Username	Problem	Language	Result	Execution time	Memory
611768		Jomnoi	Highway Tolls (IOI18_highway)	C++17	12 / 100	142 ms	9064 KiB

highway

#include <bits/stdc++.h>
#include "highway.h"
using namespace std;

// subtask 1, 2

const int MAX_N = 9e4 + 5;

int S, T;
long long result;
vector <int> U, V, W;
vector <int> graph[MAX_N];
vector <int> canbeanswer;
int holdedge[MAX_N];

void dfs(int u, int p, int depth) {
    if(depth == 0) {
        canbeanswer.push_back(u);
        return;
    }
    for(auto i : graph[u]) {
        int v = u ^ U[i] ^ V[i];
        if(v != p) {
            holdedge[v] = i;
            dfs(v, u, depth - 1);
        }
    }
}

void dfs2(int u, int p) {
    canbeanswer.push_back(u);
    for(auto i : graph[u]) {
        int v = u ^ U[i] ^ V[i];
        if(v != p) {
            holdedge[v] = i;
            dfs2(v, u);
        }
    }
}

void find_pair(int N, vector <int> u, vector <int> v, int A, int B) {
    int M = u.size();
    U.resize(M);
    V.resize(M);
    W.resize(M, 0);
    bool sub3 = true;
    for(int i = 0; i < M; i++) {
        U[i] = u[i], V[i] = v[i];
        graph[U[i]].push_back(i);
        graph[V[i]].push_back(i);

        if(U[i] != i or V[i] != i + 1) {
            sub3 = false;
        }
    }
    
    if(sub3 == true) {
        int rt;
        for(int i = 0; i < N; i++) {
            if(graph[i].size() == 1) {
                rt = i;
            }
        }

        dfs2(rt, -1);

        W.resize(M, 1);
        long long need = ask(W);

        int l = 1, r = N - 1;
        while(l <= r) {
            int mid = (l + r) / 2;

            W.clear();
            W.resize(M, 0);
            for(int i = 1; i <= mid; i++) {
                W[holdedge[canbeanswer[i]]] = 1;
            }

            result = ask(W);
            if(result < need) {
                l = mid + 1;
            }
            else {
                r = mid - 1;
                S = mid;
            }
        }

        l = 1, r = S - 1;
        while(l <= r) {
            int mid = (l + r) / 2;

            W.clear();
            W.resize(M, 0);
            for(int i = mid; i <= S; i++) {
                W[holdedge[canbeanswer[i]]] = 1;
            }

            result = ask(W);
            if(result < need) {
                r = mid - 1;
            }
            else {
                l = mid + 1;
                T = mid;
            }
        }
        answer(canbeanswer[S], canbeanswer[T]);
    }
    else { // sub12
        S = 0;
        result = ask(W);

        int numberofEdge = result / A;

        dfs(0, -1, numberofEdge);

        int l = 0, r = canbeanswer.size() - 1;
        while(l <= r) {
            int mid = (l + r) / 2;

            W.clear();
            W.resize(M, 0);
            for(int i = 0; i <= mid; i++) {
                W[holdedge[canbeanswer[i]]] = 1;
            }

            result = ask(W);
            if(result == 1ll*numberofEdge * A) {
                l = mid + 1;
            }
            else {
                r = mid - 1;
                T = mid;
            }
        }
        answer(S, canbeanswer[T]);
    }
}

Compilation message (stderr)

highway.cpp: In function 'void find_pair(int, std::vector<int>, std::vector<int>, int, int)':
highway.cpp:65:13: warning: 'rt' may be used uninitialized in this function [-Wmaybe-uninitialized]
   65 |         dfs2(rt, -1);
      |         ~~~~^~~~~~~~

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