제출 #1048869

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1048869		Alihan_8	통행료 (IOI18_highway)	C++17	100 / 100	128 ms	11928 KiB

highway

#include "highway.h"

#include <bits/stdc++.h>

using namespace std;

#define all(x) x.begin(), x.end()
#define ar array
#define pb push_back
#define ln '\n'
//#define int long long

using i64 = long long;

template <class F, class _S>
bool chmin(F &u, const _S &v){
    bool flag = false;
    if ( u > v ){
        u = v; flag |= true;
    }
    return flag;
}

template <class F, class _S>
bool chmax(F &u, const _S &v){
    bool flag = false;
    if ( u < v ){
        u = v; flag |= true;
    }
    return flag;
}

void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
	int n = N, M = U.size();
	
	vector <vector<ar<int,2>>> adj(n);
	
	for ( int i = 0; i < M; i++ ){
		adj[U[i]].pb({V[i], i});
		adj[V[i]].pb({U[i], i});
	}
	
	vector <int> w(M);
	
	i64 C = ask(w);
	
	int l = 0, r = n - 1, ans;
	
	while ( l <= r ){
		int m = (l + r) / 2;
		
		if ( r - l > 60000 ) m = 60000;
		
		w.assign(M, 0);
		
		for ( int u = m + 1; u < n; u++ ){
			for ( auto &[v, j]: adj[u] ){
				w[j] = 1;
			}
		}
		
		if ( ask(w) == C ){
			ans = m;
			r = m - 1;
		} else l = m + 1;
	}
	
	int root = ans;
	
	vector <int> fa(n), ls, us(n);
	
	queue <int> q;
	
	q.push(root); us[root] = 1;
	
	while ( !q.empty() ){
		int u = q.front();
		q.pop();
		
		ls.pb(u);
		
		for ( auto &[v, j]: adj[u] ){
			if ( us[v] ) continue;
			
			us[v] = 1;
			fa[v] = u;
			q.push(v);
		}
	}
	
	vector <int> e(n, -1);
	
	for ( int u = 0; u < n; u++ ){
		for ( auto &[v, j]: adj[u] ){
			if ( fa[u] == v ){
				e[u] = j;
			}
		}
	}
	
	l = 1, r = n - 1;
	
	while ( l <= r ){
		int m = (l + r) / 2;
		
		if ( r - l > 60000 ) m = 60000;
		
		w.assign(M, 1);
		
		for ( int i = 1; i <= m; i++ ){
			w[e[ls[i]]] = 0;
		}
		
		if ( ask(w) == C ){
			ans = m;
			r = m - 1;
		} else l = m + 1;
	}
	
	int sx = ls[ans];
	
	vector <int> pth;
	
	{ // path from sx to root
		int it = sx;
		
		while ( it != root ){
			pth.pb(e[it]);
			it = fa[it];
		}
	}
	
	l = 0, r = ans - 1;
	
	while ( l <= r ){
		int m = (l + r) / 2;
		
		w.assign(M, 1);
		
		for ( auto &j: pth ) w[j] = 0;
		
		for ( int i = 0; i < m; i++ ){
			w[e[ls[i + 1]]] = 0;
		}
		
		if ( ask(w) == C ){
			ans = m;
			r = m - 1;
		} else l = m + 1;
	}
	
	int se = ls[ans];
	
	answer(sx, se);
}

컴파일 시 표준 에러 (stderr) 메시지

highway.cpp: In function 'void find_pair(int, std::vector<int>, std::vector<int>, int, int)':
highway.cpp:127:14: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
  127 |   while ( it != root ){
      |           ~~~^~~~~~~

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