Submission #333429

#	Time	Username	Problem	Language	Result	Execution time	Memory
333429		SHZhang	Highway Tolls (IOI18_highway)	C++14	90 / 100	315 ms	12840 KiB

highway

#include <cstdio>
#include <utility>
#include <vector>
#include <queue>
#include "highway.h"

using namespace std;

#define ll long long

vector<pair<int, int> > graph[150000];

int n, m; ll mindis;

void bfs(int node, vector<pair<int, int> >& seq)
{
    queue<int> que; que.push(node);
    vector<int> dist(n);
    for (int i = 0; i < n; i++) dist[i] = 100000000;
    dist[node] = 0;
    seq.push_back(make_pair(node, -1));
    while (!que.empty()) {
        int cur = que.front(); que.pop();
        for (int i = 0; i < graph[cur].size(); i++) {
            int nxt = graph[cur][i].first;
            if (dist[cur] + 1 < dist[nxt]) {
                dist[nxt] = dist[cur] + 1;
                que.push(nxt); seq.push_back(make_pair(nxt, graph[cur][i].second));
            }
        }
    }
}

int binary_search(vector<pair<int, int> >& seq)
{
    int l = 0; int r = n - 1;
    while (l < r) {
        vector<int> wt(m);
        for (int i = 0; i < m; i++) wt[i] = 1;
        int mid = (l + r) / 2;
        for (int i = 1; i <= mid; i++) {
            wt[seq[i].second] = 0;
        }
        ll dis = ask(wt);
        if (dis == mindis) {
            r = mid;
        } else {
            l = mid + 1;
        }
    }
    return seq[l].first;
}

void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
    n = N; m = U.size();
    for (int i = 0; i < m; i++) {
        graph[U[i]].push_back(make_pair(V[i], i));
        graph[V[i]].push_back(make_pair(U[i], i));
    }
    int l = 0; int r = n - 1;
    vector<int> wt(m);
    for (int i = 0; i < m; i++) wt[i] = 0;
    mindis = ask(wt);
    //fprintf(stderr, "here1");
    while (l < r) {
        vector<int> wt(m);
        for (int i = 0; i < m; i++) wt[i] = 0;
        int mid = (l + r) / 2;
        for (int i = 0; i <= mid; i++) {
            for (int j = 0; j < graph[i].size(); j++) {
                wt[graph[i][j].second] = 1;
            }
        }
        ll dis = ask(wt);
        if (dis == mindis) {
            l = mid + 1;
        } else {
            r = mid;
        }
    }
    //fprintf(stderr, "here");
    int midnode = l;
    vector<pair<int, int> > seq; bfs(midnode, seq);
    int S = binary_search(seq);
    seq.clear();
    bfs(S, seq);
    int T = binary_search(seq);
    answer(S, T);
}

Compilation message (stderr)

highway.cpp: In function 'void bfs(int, std::vector<std::pair<int, int> >&)':
highway.cpp:24:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |         for (int i = 0; i < graph[cur].size(); i++) {
      |                         ~~^~~~~~~~~~~~~~~~~~~
highway.cpp: In function 'void find_pair(int, std::vector<int>, std::vector<int>, int, int)':
highway.cpp:70:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   70 |             for (int j = 0; j < graph[i].size(); j++) {
      |                             ~~^~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 7 / 7
• Subtask 3: 6 / 6
• Subtask 4: 33 / 33
• Subtask 5: 18 / 18
• Subtask 6: 21 / 31