답안 #118692

# 제출 시각 아이디 문제 언어 결과 실행 시간 메모리
118692 2019-06-19T11:40:01 Z someone_aa 통행료 (IOI18_highway) C++17
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#include "highway.h"
#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define mp make_pair
using namespace std;
const int maxn = 100100;
int n, m;
vector<int>w;
vector<int>gs[maxn];
vector<pair<int,int> > g[maxn];

vector<int>gt[maxn];

int dist[maxn][2], parent[maxn][2];
bool visited[maxn];

ll dista;

map<pair<int,int>, int> ind;

void bfs1(int st, int d) {
    memset(visited,false,sizeof(visited));
    queue<int>q;
    q.push(st);

    parent[st][d] = -1;
    visited[st] = true;

    while(!q.empty()) {
        int curr = q.front();
        q.pop();

        for(auto i:g[curr]) {
            if(!visited[i.first]) {
                visited[i.first] = true;
                dist[i.first][d] = dist[curr][d] + 1;
                parent[i.first][d] = i.second;
                q.push(i.first);
            }
        }
    }
}

set<pair<int,int> > sta, stb;

void preprocess() {
    for(int i=0;i<n;i++) {
        if(dist[i][0] == dist[i][1]) continue; // skip this node

        if(dist[i][0] < dist[i][1]) {
            for(int j:gs[i]) {
                if(dist[j][0] < dist[j][1]) {
                    sta.insert(mp(min(i, j), max(i, j)));
                }
            }
        }
        else {
            for(int j:gs[i]) {
                if(dist[j][0] > dist[j][1]) {
                    stb.insert(mp(min(i, j), max(i, j)));
                }
            }
        }
    }
}


int solve(int root, int d) {
    // build bfs tree
    //memset(visited,false,sizeof(visited));
    //memset(parent,-1,sizeof(parent));

    set<pair<int,int> > edges;
    if(d == 0) edges = sta;
    else edges = stb;

    for(auto i:edges) {
        gt[i.first].pb(i.second);
        gt[i.second].pb(i.first);
    }

    vector<int>v, v2;

    queue<int>q;
    q.push(root);

    visited[root] = true;
    parent[root][d] = -1;

    while(!q.empty()) {
        int curr = q.front();
        q.pop();

        v.pb(parent[curr][d]);
        v2.pb(curr);
        for(auto i:gt[curr]) {
            if(!visited[i]) {
                visited[i] = true;
                parent[i][d] = curr;
                dist[i][d] = dist[curr][d] + 1;
                q.push(i);
            }
        }
    }

    if(v.size() == 1) return v2[0];
    // perform binary search

    for(int i=0;i<v.size();i++) {
        if(v[i] == -1) continue; // root
        int cind = ind[mp(v[i], v2[i])];
        w[cind] = 1;
    }

    int li = 0, ri = v.size() - 1;

    while(li < ri) {
        int mid = (li + ri) / 2;

        // all before mid put them as low cost and other as high cost
        for(int i=0;i<=mid;i++) {
            if(v[i] == -1) continue; // root
            int cind = ind[mp(v[i], v2[i])];
            w[cind] = 0;
        }

        ll cdist = ask(w);
        for(int i=0;i<=mid;i++) {
            if(v[i] == -1) continue; // root
            int cind = ind[mp(v[i], v2[i])];
            w[cind] = 1;
        }

        if(cdist == dista) {
            ri = mid;
        }
        else {
            li = mid + 1;
        }
    }

    for(int i=0;i<v.size();i++) {
        if(v[i] == -1) continue; // root
        int cind = ind[mp(v[i], v2[i])];
        w[cind] = 0;
    }

    return v2[li];
}

void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
    n = N; m = U.size();
    int li=0, ri=m-1;

    for(int i=0;i<m;i++) {
        ind[mp(U[i], V[i])] = ind[mp(V[i], U[i])] = i;
        gs[U[i]].pb(V[i]);
        gs[V[i]].pb(U[i]);

        g[U[i]].pb(mp(V[i], i));
        g[V[i]].pb(mp(U[i], i));

        w.pb(0);
    }

    dista = ask(w);
    while(li<ri) {
        int mid = (li+ri)/2;
        for(int i=li;i<=mid;i++) {
            w[i] = 1;
        }
        ll distb = ask(w);
        for(int i=li;i<=mid;i++) {
            w[i] = 0;
        }

        if(dista == distb) {
            li = mid + 1;
        }
        else {
            ri = mid;
        }
    }
    int x = li;
    int u = U[x], v = V[x];

    //cout<<u<<" "<<v<<"\n";

    bfs1(u, 0);
    bfs2(v, 1);
    preprocess();

    memset(visited,false,sizeof(visited));
    //cout<<"Ans: "<<xx<<" "<<yy<<"\n";
    answer(solve(u, 0), solve(v, 1));
}

Compilation message

highway.cpp: In function 'int solve(int, int)':
highway.cpp:110:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<v.size();i++) {
                 ~^~~~~~~~~
highway.cpp:143:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<v.size();i++) {
                 ~^~~~~~~~~
highway.cpp: In function 'void find_pair(int, std::vector<int>, std::vector<int>, int, int)':
highway.cpp:191:5: error: 'bfs2' was not declared in this scope
     bfs2(v, 1);
     ^~~~
highway.cpp:191:5: note: suggested alternative: 'bfs1'
     bfs2(v, 1);
     ^~~~
     bfs1