Submission #53347

#	Time	Username	Problem	Language	Result	Execution time	Memory
53347		junodeveloper	Boat (APIO16_boat)	C++11	100 / 100	1059 ms	11052 KiB

boat

#include <bits/stdc++.h>
#define SZ(x) ((int)x.size())
#define ALL(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
typedef long double ld;
const int MOD = 1e9 + 7;
int n, a[510], b[510];
int dp[510][1010], dp2[510][1010];
int sum[1010][510], scnt[1010][510], fac[510]={1}, inv[510]={1}, bigfac[1010][510];
vector<int> Vx;
int modpow(int a, long long n, int mod = MOD) {
	int r = 1, b = a;
	while(n > 0) {
		if(n & 1) r = 1ll * r * b % mod;
		b = 1ll * b * b % mod;
		n >>= 1;
	}
	return r;
}
int main() {
	scanf("%d", &n);
	for(int i=1; i<=n; i++) {
		scanf("%d%d", a+i, b+i); b[i]++;
		Vx.push_back(a[i]);
		Vx.push_back(b[i]);
	}
	sort(ALL(Vx));
	Vx.erase(unique(ALL(Vx)), Vx.end());
	for(int i=1; i<=500; i++) { 
		fac[i] = 1ll * fac[i-1] * i % MOD;
		inv[i] = modpow(fac[i], MOD - 2);
	}
	for(int i=1; i<SZ(Vx); i++) {
		int len = Vx[i] - Vx[i-1];
		bigfac[i][0] = 1;
		for(int j=1; j<=n; j++) {
			scnt[i][j] = scnt[i][j-1] + (min(b[j], Vx[i]) - max(a[j], Vx[i-1]) > 0);
			bigfac[i][j] = 1ll * bigfac[i][j-1] * (len - j + 1) % MOD;
		}
		for(int j=1; j<=scnt[i][n]; j++)
			for(int k=1; k<=j; k++)
				sum[i][j] = (sum[i][j] + 1ll
				* fac[j-1] * inv[k-1] % MOD * inv[j-k] % MOD
				* bigfac[i][k] % MOD * inv[k]) % MOD;
	}
	int res = 0;
	for(int i=1; i<=n; i++) {
		for(int j=1; j<SZ(Vx); j++) {
			if(!(min(b[i], Vx[j]) - max(a[i], Vx[j-1]) > 0)) continue;
			dp[i][j] = sum[j][scnt[j][i]];
			for(int k=1; k<i; k++)
				dp[i][j] = (dp[i][j] + 1ll * dp2[k][j-1] * sum[j][scnt[j][i] - scnt[j][k]]) % MOD;
			res = (res + dp[i][j]) % MOD;
		}
		for(int j=1; j<SZ(Vx); j++) dp2[i][j] = (dp2[i][j-1] + dp[i][j]) % MOD;
	}
	// sum[s][cnt] : sum(C(cnt-1, i-1) * C(Vx[s]-Vx[s-1], i)) for 1<=i<=cnt
	printf("%d", res);
	return 0;
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:22:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~
boat.cpp:24:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", a+i, b+i); b[i]++;
   ~~~~~^~~~~~~~~~~~~~~~~~

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