Submission #640385

#	Time	Username	Problem	Language	Result	Execution time	Memory
640385		imtore	Boat (APIO16_boat)	C++17	9 / 100	72 ms	2348 KiB

boat

#include <stdio.h>
#include <vector>
#include <algorithm>
#define ll long long
#define MOD 1'000'000'007
using namespace std;

int A[521], B[521];

vector<int> X;

ll inv[521];
ll dp1[521], dp2[521][521], sum[521];

ll get_inv(ll x, ll y = MOD-2){
	ll z = y & 1 ? x : 1;
	while(y >>= 1){
		if(y & 1) z = z*x%MOD;
		x = x*x%MOD;
	}
	return z;
}

int main(){
	int n; scanf("%d", &n);
	for(int i = 1; i <= n; i++) scanf("%d %d", &A[i], &B[i]);

	for(int i = 1; i <= n; i++){
		X.push_back(A[i]);
		X.push_back(B[i]+1);
	}
	sort(X.begin(), X.end());
	X.erase(unique(X.begin(), X.end()), X.end());

	for(int i = 1; i <= n; i++){
		A[i] = lower_bound(X.begin(), X.end(), A[i])-X.begin()+1;
		B[i] = lower_bound(X.begin(), X.end(), B[i]+1)-X.begin();
	}

	for(int i = 1; i <= n; i++) inv[i] = get_inv(i);

	dp1[0] = 1;
	for(int i = 1; i < X.size(); i++){
		for(int j = 0; j <= n; j++) dp2[j][0] = dp1[j];
		fill(sum, sum+n+1, 0);
		
		int cnt = 0;
		sum[0] = dp2[0][0];
		for(int j = 1; j <= n; j++){
			if(A[j] <= i && B[j] >= i){
				int l = X[i]-X[i-1]; cnt++;
				for(int k = min(cnt, l); k >= 1; k--){
					dp2[j][k] = sum[k-1]*(l-k+1)%MOD*inv[k]%MOD;
					sum[k] = (sum[k]+dp2[j][k])%MOD;
				}
			}
			sum[0] = (sum[0]+dp2[j][0])%MOD;
		}
/*
		printf("%d\n", i);
		for(int j = 0; j <= n; j++){
			for(int k = 0; k <= min(cnt, X[i]-X[i-1]); k++) printf("%lld ", dp2[j][k]);
			printf("\n");
		}
		printf("\n");
*/
		cnt = 0;
		for(int j = 1; j <= n; j++){
			dp1[j] = dp2[j][0];
			if(A[j] <= i && B[j] >= i){
				cnt++;
				for(int k = 1; k <= cnt; k++) dp1[j] = (dp1[j]+dp2[j][k])%MOD;	
			}
		}
	}
	
	ll ans = 0;
	for(int i = 1; i <= n; i++) ans = (ans+dp1[i])%MOD;
	printf("%lld", ans);

	return 0;
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:43:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   43 |  for(int i = 1; i < X.size(); i++){
      |                 ~~^~~~~~~~~~
boat.cpp:25:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   25 |  int n; scanf("%d", &n);
      |         ~~~~~^~~~~~~~~~
boat.cpp:26:35: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   26 |  for(int i = 1; i <= n; i++) scanf("%d %d", &A[i], &B[i]);
      |                              ~~~~~^~~~~~~~~~~~~~~~~~~~~~~

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