Submission #41596

#	Time	Username	Problem	Language	Result	Execution time	Memory
41596		gabrielsimoes	Boat (APIO16_boat)	C++14	0 / 100	8 ms	576 KiB

boat

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

typedef long long ll;
const ll MOD = 1000000007;
const int MAXN = 510;

ll fastpow(ll a, ll b) {
  ll result = 1;
  ll cur = a;
  while (b) {
    if (b & 1) result = (result * cur) % MOD;
    cur = (cur * cur) % MOD;
    b >>= 1;
  }
  return result;
}

int n;
int va[MAXN], vb[MAXN];
ll dp[MAXN], sum[MAXN];
vector<int> splits;
vector<ll> v;
ll inv[MAXN];

ll bin(ll a, ll b) {
  ll result = 1;
  while (a && b) result = (result * (a--) * inv[b--]);
  return result;
}

int main() {
  for (int i = 1; i < MAXN; i++) inv[i] = fastpow(i, MOD - 2);

  scanf("%d", &n);

  for (int i = 1; i <= n; i++) {
    scanf("%d %d", &va[i], &vb[i]);
    vb[i]++;
    splits.push_back(va[i]);
    splits.push_back(vb[i]);
  }

  sort(splits.begin(), splits.end());
  splits.resize(unique(splits.begin(), splits.end()) - splits.begin());

  for (int i = 1; i <= n; i++) {
    va[i] = (lower_bound(splits.begin(), splits.end(), va[i]) - splits.begin());
    vb[i] = (lower_bound(splits.begin(), splits.end(), vb[i]) - splits.begin());
  }

  for (int split = 1; split < splits.size(); split++) {
    ll splitSize = splits[split] - splits[split - 1];

    sum[0] = 1;
    for (int i = 1; i <= n; i++) sum[i] = (sum[i - 1] + dp[i]) % MOD;
    v.clear();

    // printf("split %d: [%d, %d)\n", split, splits[split - 1], splits[split]);

    for (int i = 1; i <= n; i++) {
      if (va[i] < split && vb[i] >= split) {
        v.push_back(sum[i - 1]);

        for (auto p = v.rbegin(); p != v.rend(); p++) {
          int cnt = (p - v.rbegin()) + 1;
          if (cnt > 1)
            dp[i] = (dp[i] + (*p) * bin(splitSize + cnt - 2, cnt)) % MOD;
          else
            dp[i] = (dp[i] + (*p) * splitSize) % MOD;
        }
      }

      // printf("dp[%d][%d] == %lld\n", split, i, dp[i]);
    }
  }

  ll ans = 0;
  for (int i = 1; i <= n; i++) ans = (ans + dp[i]) % MOD;

  printf("%lld\n", ans);
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:52:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int split = 1; split < splits.size(); split++) {
                             ^
boat.cpp:35:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &n);
                  ^
boat.cpp:38:35: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d", &va[i], &vb[i]);
                                   ^

• Subtask 1: 0 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42