Submission #952221

#	Time	Username	Problem	Language	Result	Execution time	Memory
952221		nguyennh	Bigger segments (IZhO19_segments)	C++14	13 / 100	35 ms	2392 KiB

segments

#include<bits/stdc++.h>
#define el '\n'
using namespace std ;

mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());

const int64_t inf = 1e18;
const int MN = 5e5 + 5;

int a[MN] , n;

namespace sub_trau{
  int x[25] , ans = 0;
  
  void backtrack(int k){
    if (k > n - 1){
      int cur = 0 , sum = 0 , cnt = 0;
      bool check = true;
      for ( int i = 1 ; i <= n; i++ ){
        sum += a[i];
        if (x[i] == 1){
          if (sum < cur){
            check = false;
            break;
          }
          cnt++;
          cur = sum;
          sum = 0;
        }
      }
      if (check) ans = max(ans , cnt);
      return;
    }
    for ( int i = 0 ; i <= 1 ; i++ ){
      x[k] = i;
      backtrack(k + 1);
    }
  }
  
  void solve(){
    x[n] = 1;
    backtrack(1);
    cout << ans;
  }
}

namespace sub2{
  void solve(){
    vector<int64_t> pref(n + 5);
    vector<bool> is_greater(n + 5 , false);
    deque<int> dq;
    for ( int i = 1 ; i <= n ; i++ ){
      while (!dq.empty() && dq.back() <= a[i]) dq.pop_back();
      if (dq.size() && dq.front() > a[i]) is_greater[i] = true;
      dq.push_back(a[i]);
    }
    for ( int i = 1 ; i <= n ; i++ ) pref[i] = pref[i - 1] + a[i];
    vector<vector<int64_t>> dp(n + 5 , vector<int64_t>(n + 5));
    for ( int i = 1 ; i <= n ; i++ ){
      for ( int j = i - is_greater[i] ; j >= 1 ; j-- ){
        int l = 0 , r = j , pos = -1;
        while (l <= r){
          int mid = l + r >> 1;
          if (pref[j - 1] - pref[mid - 1] <= pref[i] - pref[j - 1]){
            pos = mid;
            r = mid - 1;
          }
          else l = mid + 1;
        } 
        assert(pos != -1);
        for ( int k = pos ; k <= j - 1 ; k++ ) {
          if (is_greater[j - 1] && k == j - 1) continue;
          dp[i][j] = max(dp[i][j] , dp[j - 1][k] + 1);
        }
      }
    }
    int64_t ans = 0;
    for ( int i = 1 ; i <= n ; i++ ){
      ans = max(ans , dp[n][i]);
    }
    cout << ans;
  }
}

int32_t main (){
//  freopen("segments.inp" , "r" , stdin);
//  freopen("segments.out" , "w" , stdout);
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for ( int i = 1 ; i <= n ; i++ ) cin >> a[i];
  if (n <= 20){
    sub_trau::solve();
    return 0;
  }
  if (n <= 3000){
    sub2::solve();
    return 0;
  }
}

Compilation message (stderr)

segments.cpp: In function 'void sub2::solve()':
segments.cpp:63:23: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   63 |           int mid = l + r >> 1;
      |                     ~~^~~

• Subtask 1: 13 / 13
• Subtask 2: 0 / 14
• Subtask 3: 0 / 10
• Subtask 4: 0 / 36
• Subtask 5: 0 / 27