Submission #312368

#	Time	Username	Problem	Language	Result	Execution time	Memory
312368		VROOM_VARUN	Sparklers (JOI17_sparklers)	C++14	100 / 100	76 ms	3172 KiB

sparklers

/*
ID: varunra2
LANG: C++
TASK: sparklers
*/

#include <bits/stdc++.h>
using namespace std;

#ifdef DEBUG
#include "lib/debug.h"
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define debug_arr(...) \
  cerr << "[" << #__VA_ARGS__ << "]:", debug_arr(__VA_ARGS__)
#pragma GCC diagnostic ignored "-Wsign-compare"
//#pragma GCC diagnostic ignored "-Wunused-parameter"
//#pragma GCC diagnostic ignored "-Wunused-variable"
#else
#define debug(...) 42
#endif

#define int long long
#define EPS 1e-9
#define IN(A, B, C) assert(B <= A && A <= C)
#define INF (int)1e9
#define MEM(a, b) memset(a, (b), sizeof(a))
#define MOD 1000000007
#define MP make_pair
#define PB push_back
#define all(cont) cont.begin(), cont.end()
#define rall(cont) cont.end(), cont.begin()
#define x first
#define y second

const double PI = acos(-1.0);
typedef long long ll;
typedef long double ld;
typedef pair<int, int> PII;
typedef map<int, int> MPII;
typedef multiset<int> MSETI;
typedef set<int> SETI;
typedef set<string> SETS;
typedef vector<int> VI;
typedef vector<PII> VII;
typedef vector<VI> VVI;
typedef vector<string> VS;

#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define trav(a, x) for (auto& a : x)
#define sz(x) (int)(x).size()
typedef pair<int, int> pii;
typedef vector<int> vi;
#pragma GCC diagnostic ignored "-Wsign-compare"
// util functions
// const int N = 1005;
int n, k, t;
int v;
VI vals;
// VVI dp(N, VI(N, -1));

void init() { vals.resize(n); }

// bool solve(int l, int r) {
//   if (l > k) return false;
//   if (r < k) return false;
//   if (l == r) return true;

//   if (dp[l][r] != -1) return dp[l][r];

//   if (vals[r] - vals[l] <= 2 * (r - l) * t * v) {
//     if (solve(l, r - 1))
//       dp[l][r] = 1;
//     else if (solve(l + 1, r))
//       dp[l][r] = 1;
//     else
//       dp[l][r] = 0;
//   } else {
//     dp[l][r] = 0;
//   }

//   return dp[l][r];
// }

// void fll(VVI& dp, int val) { trav(x, dp) trav(y, x) y = val; }

bool check(VI& a, VI& b) {
  int l1, l2, r1, r2;

  l1 = l2 = r1 = r2 = 0;

  bool moved = true;

  while (moved) {
    moved = false;
    while (l2 + 1 < sz(a) and a[l2 + 1] >= b[r1]) {
      moved = true;
      if (a[++l2] > a[l1]) l1 = l2;
    }
    while (r2 + 1 < sz(b) and a[l1] >= b[r2 + 1]) {
      moved = true;
      if (b[++r2] < b[r1]) r1 = r2;
    }
  }

  return l2 + 1 == sz(a) and r2 + 1 == sz(b);
}

bool works(int _v) {
  v = _v;
  if (v * t >= vals.back()) return true;
  VI a, b;

  for (int i = k; i >= 0; i--) {
    a.PB(vals[i] - 2 * v * t * i);
  }

  for (int i = k; i < n; i++) {
    b.PB(vals[i] - 2 * v * t * i);
  }

  if (!check(a, b)) return false;
  reverse(all(a));
  reverse(all(b));
  if (!check(a, b)) return false;
  return true;

  // // fll(dp, -1);
  // dp[k][k] = 1;
  // return solve(0, n - 1);
}

int32_t main() {
  // #ifndef ONLINE_JUDGE
  // freopen("sparklers.in", "r", stdin);
  // freopen("sparklers.out", "w", stdout);
  // #endif
  cin.sync_with_stdio(0);
  cin.tie(0);

  cin >> n >> k >> t;

  k--;

  init();

  for (int i = 0; i < n; i++) {
    cin >> vals[i];
  }

  int x = -1;

  for (int b = INF + 1; b >= 1; b /= 2) {
    while (!works(x + b)) x += b;
  }

  cout << x + 1 << '\n';

  return 0;
}

• Subtask 1: 30 / 30
• Subtask 2: 20 / 20
• Subtask 3: 50 / 50