Submission #101067

#	Time	Username	Problem	Language	Result	Execution time	Memory
101067		ecasdqina	Tents (JOI18_tents)	C++14	100 / 100	323 ms	71032 KiB

tents

#include <bits/stdc++.h>
using namespace std::literals::string_literals;
using i64 = long long;
using std::cout;
using std::endl;
using std::cin;
 
const int MOD = 1e9 + 7;
 
i64 mod_pow(i64 x, i64 n = MOD - 2) {
	i64 ret = 1;
	while(n) {
		if(n & 1) (ret *= x) %= MOD;
		(x *= x) %= MOD;
		n >>= 1;
	}
	return ret;
}
 
std::vector<i64> fact, inv;
i64 comb(int n, int r) {
	return fact[n] * inv[n - r] % MOD * inv[r] % MOD;
}
 
int main() {
	int h, w; scanf("%d%d", &h, &w);
	
//	assert(h <= 300 and w <= 300);
	
	fact.assign(std::max(h, w) + 1, 1); inv.assign(std::max(h, w) + 1, 1);
	for(int i = 0; i < std::max(h, w); i++) fact[i + 1] = fact[i] * (i64)(i + 1) % MOD;
	for(int i = 0; i <= std::max(h, w); i++) inv[i] = mod_pow(fact[i]);
	
	std::vector<std::vector<i64>> dp(h + 1, std::vector<i64>(w + 1, 0));
	dp[h][w] = 1;
	for(i64 i = h; i >= 0; i--) {
		for(i64 j = w; j >= 0; j--) {
			if(i >= 1 and j >= 1) {
				dp[i - 1][j - 1] += dp[i][j] * j % MOD * 4;
				dp[i - 1][j - 1] %= MOD;
			}
			if(i >= 1 and j >= 2) {
				dp[i - 1][j - 2] += dp[i][j] * comb(j, 2) % MOD;
				dp[i - 1][j - 2] %= MOD;
			}
			if(i >= 2 and j >= 1) {
				dp[i - 2][j - 1] += dp[i][j] * j % MOD * (i - 1) % MOD;
				dp[i - 2][j - 1] %= MOD;
			}
			if(i >= 1) {
				dp[i - 1][j] += dp[i][j];
				dp[i - 1][j] %= MOD;
			}
		}
	}
	
	i64 ans = 0;
	for(int j = 0; j <= w; j++) (ans += dp[0][j]) %= MOD;
	printf("%lld\n", (ans - 1 + MOD) % MOD);
	return 0;
}

Compilation message (stderr)

tents.cpp: In function 'int main()':
tents.cpp:26:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  int h, w; scanf("%d%d", &h, &w);
            ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 48 / 48
• Subtask 2: 52 / 52