#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
