1039B - Subway Pursuit - CodeForces Solution

#include <algorithm>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#ifdef DEBUG
#include <time.h>
#endif

#define all(a) (a).begin(), (a).end()
#define rev(a) (a).rbegin(), (a).rend()
#define F first
#define S second
int recur_depth = 0;
#ifdef DEBUG
#define dbg(x)                                                                 \
  {                                                                            \
    ++recur_depth;                                                             \
    auto x_ = x;                                                               \
    --recur_depth;                                                             \
    cerr << string(recur_depth, '\t') << "\e[91m" << __func__ << ":"           \
         << __LINE__ << "\t" << #x << " = " << x_ << "\e[39m" << endl;         \
  }
#else
#define dbg(x)
#endif

using namespace std;
using namespace __gnu_pbds;

typedef pair<int, int> ii;

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> llll;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pair<int, int>> vii;
typedef vector<vii> vvii;

typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<pair<ll, ll>> vll;
typedef vector<vll> vvll;

typedef vector<bool> vb;

template <class type1>
using ordered_set = tree<type1, null_type, less<type1>, rb_tree_tag,
                         tree_order_statistics_node_update>;

template <typename A, typename B>
ostream &operator<<(ostream &os, const pair<A, B> &p) {
  return os << '(' << p.first << ", " << p.second << ')';
}
template <typename T_container, typename T = typename enable_if<
                                    !is_same<T_container, string>::value,
                                    typename T_container::value_type>::type>
ostream &operator<<(ostream &os, const T_container &v) {
  os << '{';
  string sep;
  for (const T &x : v)
    os << sep << x, sep = ", ";
  return os << '}';
}

const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
const ll INF = 1e9;
const ld EPS = 1e-9;

void solve() {
  ll n, k;
  cin >> n >> k;

  auto ask = [](ll l, ll r) -> bool {
    cout << l << " " << r << endl;

    string s;
    cin >> s;

    if (s[0] == 'B')
      exit(0);

    if (s[0] == 'Y' && l == r)
      exit(0);

    return s[0] == 'Y';
  };

  if (k == 0) {
    ll l = 1, r = n;
    while (l <= r) {
      ll mid = (l + r) / 2;
      if (ask(l, mid)) {
        r = mid;
      } else {
        l = mid + 1;
      }
    }
    assert(0);
    return;
  }

  random_device rd;
  mt19937 gen(rd());
  uniform_int_distribution<> dis(0, 4 * k - 1);

  ll l = 1, r = n;
  while (l <= r) {
    if (r - l + 1 <= 4 * k) {
      ll id = l + dis(gen);
      while (!(l <= id && id <= r))
        id = l + dis(gen);
      ask(id, id);
      l = max(1LL, l - k), r = min(n, r + k);
      continue;
    }

    ll mid = (l + r) / 2;
    if (ask(l, mid))
      r = mid;
    else
      l = mid + 1;
    l = max(1LL, l - k);
    r = min(n, r + k);
  }
  assert(0);
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);

  clock_t start = clock();

  int test_cases = 1;
  // cin >> test_cases;

  while (test_cases--)
    solve();

#ifdef DEBUG
  cerr << fixed << setprecision(10)
       << "\nTime Taken: " << (double)(clock() - start) / CLOCKS_PER_SEC
       << "s\n";
#endif
  return 0;
}