Codeforces Round #499 (Div. 2) D. Rocket

問題ページ
Problem - D - Codeforces

考えたこと

• p[i]を把握しないといけない
• y=INFを出力しようと思ったけどだめなのでy=1を出力して確認する
• p[i]さえわかれば二分探索すればよい
• m<=10^9ならクエリ回数30回あれば足りる
• 二分探索を実装して出すと通る

y=1を出力するのに気づけるかどうか、この問題いる？

ソースコード

#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll INF = (1LL<<60);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a<=x&&x<b; }
template<typename T> T ceil(T a, T b) { return a/b + !!(a%b); }
template<class S,class T>
ostream &operator <<(ostream& out,const pair<S,T>& a){
  out<<'('<<a.first<<','<<a.second<<')';
  return out;
}
template<class T>
ostream &operator <<(ostream& out,const vector<T>& a){
  out<<'[';
  REP(i, a.size()) {out<<a[i];if(i!=a.size()-1)out<<',';}
  out<<']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

// #define DEBUG
int m, n;
int x = 10, idx = 0;
int pp[30] = {1, -1, 1, -1, -1, -1};
int query(int y) {
  #ifdef DEBUG
    cout << "out:" << y << endl;
    if(y == x) {cout << 0 << endl; idx++; exit(0);}
    else if(x < y) {cout << -1*pp[idx%n] << endl; idx++; return 0;}
    else {cout << 1*pp[idx%n] << endl; idx++; return 1;}
  #else
    cout << y << endl;
    int res;
    cin >> res;
    if(res == 1) return 1;
    else if(res == -1) return -1;
    else exit(0);
  #endif
}

signed main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> m >> n;

  VI p(n);
  REP(i, n) {
    if(query(1) == 1) p[i] = 1;
    else p[i] = 0;
  }

  // [lb, ub]
  int lb = 1, ub = m;
  REP(i, 60-n) {
    int mid = (lb+ub)/2;
    int ret = query(mid);
    if(p[i%n]==0) ret *= -1;
    if(ret == 1) lb = mid+1;
    else ub = mid-1;
  }

  return 0;
}