Submission #793369

#	Time	Username	Problem	Language	Result	Execution time	Memory
793369		kingfran1907	Boat (APIO16_boat)	C++14	9 / 100	145 ms	2312 KiB

boat

#include <bits/stdc++.h>

using namespace std;
typedef long long llint;

const int maxn = 1010;
const int mod = 1e9+7;

int mul(int a, int b) {
	llint out = (llint)a * b;
	return out % mod;
}

int pot(int a, int b) {
	if (b == 0) return 1;
	if (b % 2 == 1) return pot(a, b - 1);
	
	int out = pot(a, b / 2);
	return mul(out, out);
}

int n;
int a[maxn], b[maxn];
int fac[maxn];
int dp[maxn][maxn];
int inv[maxn];
int len[maxn];

int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n; i++)
		scanf("%d%d", a+i, b+i);
	vector< int > v;
	for (int i = 1; i <= n; i++) {
		v.push_back(a[i]);
		v.push_back(b[i] + 1);
	}
	sort(v.begin(), v.end());
	v.resize(unique(v.begin(), v.end()) - v.begin());
	for (int i = 1; i <= n; i++) {
		a[i] = upper_bound(v.begin(), v.end(), a[i]) - v.begin();
		b[i] = upper_bound(v.begin(), v.end(), b[i]) - v.begin();
	}
	for (int i = 0; i < v.size() - 1; i++) len[i + 1] = v[i + 1] - v[i];
	//for (int i = 0; i < v.size() - 1; i++) printf("%d ", len[i]); printf("\n\n");
	
	for (int i = 1; i <= n; i++) inv[i] = pot(i, mod - 2);
	for (int i = 0; i < v.size(); i++) dp[0][i] = 1;
	for (int i = 1; i <= n; i++) {
		for (int j = a[i]; j <= b[i]; j++) {
			if (a[i] <= j && j <= b[i]) {
				dp[i][j] = mul(len[j], dp[i - 1][j - 1]);
				int kol = 1;
				int pov = len[j] - 1;
				for (int k = i - 1; k > 0; k--) {
					if (a[k] <= j && j <= b[k]) {
						pov = mul(pov, mul(len[j] - 1 + kol, inv[kol + 1])); kol++;
						dp[i][j] += mul(dp[k - 1][j - 1], pov), dp[i][j] %= mod;
					}
				}
			}
		}
		for (int j = 0; j < v.size(); j++) {
			dp[i][j] += dp[i - 1][j], dp[i][j] %= mod;
			if (j > 0) {
				dp[i][j] += dp[i][j - 1], dp[i][j] %= mod;
				dp[i][j] += mod - dp[i - 1][j - 1], dp[i][j] %= mod;
			}
		}
		//for (int j = 0; j < v.size(); j++) printf("%d ", dp[i][j]);
		//printf("\n");
	}
	
	printf("%d\n", (mod + dp[n][v.size() - 1] - 1) % mod);
	return 0;
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:44:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   44 |  for (int i = 0; i < v.size() - 1; i++) len[i + 1] = v[i + 1] - v[i];
      |                  ~~^~~~~~~~~~~~~~
boat.cpp:48:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   48 |  for (int i = 0; i < v.size(); i++) dp[0][i] = 1;
      |                  ~~^~~~~~~~~~
boat.cpp:63:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   63 |   for (int j = 0; j < v.size(); j++) {
      |                   ~~^~~~~~~~~~
boat.cpp:30:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   30 |  scanf("%d", &n);
      |  ~~~~~^~~~~~~~~~
boat.cpp:32:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   32 |   scanf("%d%d", a+i, b+i);
      |   ~~~~~^~~~~~~~~~~~~~~~~~

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