Submission #793345

#	Time	Username	Problem	Language	Result	Execution time	Memory
793345		kingfran1907	Boat (APIO16_boat)	C++14	0 / 100	3 ms	2260 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 = 0; 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 = 0; i < n; i++) {
		a[i] = lower_bound(v.begin(), v.end(), a[i]) - v.begin();
		b[i] = lower_bound(v.begin(), v.end(), b[i] + 1) - v.begin() - 1;
	}
	for (int i = 0; i < v.size() - 1; i++) len[i] = 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() - 1; i++) dp[0][i] = 1;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j < v.size() - 1; j++) {
			dp[i][j] = dp[i][j - 1];
			if (a[i] <= j && j <= b[i]) {
				int kol = 0;
				int pov = 1;
				int suma = len[j];
				for (int k = i - 1; k >= 0; k--) {
					//printf("%d %d --> %d --- %d %d\n", i, j, k, dp[k][j - 1], suma);
					dp[i][j] += mul(dp[k][j - 1], suma), dp[i][j] %= mod;
					if (a[k] <= j && j <= b[k]) {
						pov = mul(pov, mul(len[j] - kol - 1, inv[kol + 1]));
						suma += pov, suma %= mod;
					}
				}
			}
		}
		//for (int j = 0; j < v.size() - 1; j++) printf("%d ", dp[i][j]);
		//printf("\n");
	}
	
	int sum = 0;
	for (int i = 1; i <= n; i++) sum += dp[i][v.size() - 2], sum %= mod;
	printf("%d\n", sum);
	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] = 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() - 1; i++) dp[0][i] = 1;
      |                  ~~^~~~~~~~~~~~~~
boat.cpp:50:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   50 |   for (int j = 1; j < v.size() - 1; 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: 0 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42