Submission #899070

#	Time	Username	Problem	Language	Result	Execution time	Memory
899070		lovrot	Construction of Highway (JOI18_construction)	C++17	0 / 100	71 ms	144208 KiB

construction

#include <cstdio> 
#include <cstring> 

using namespace std;

typedef long long ll; 

const int N = 3010; 
const int MOD = 1e9 + 7;

inline int add(int a, int b) {
	if(a + b < MOD) return a + b;
	return a + b - MOD; 
}

inline int mult(int a, int b) {
	return (ll) a * b % MOD;
}

inline int pot(int a, int b) {
	int ret = 1;
	for(; b; b /= 2, a = mult(a, a))
		if(b & 1) ret = mult(ret, a);
	return ret;
}

inline int inv(int a) {
	return pot(a, MOD - 2);
}

int w, h;

int C[N][N], F[N][N];

int f(int a, int b) {
	if(!a || !b) return 1;
	if(F[a][b] != -1) return F[a][b];
	return F[a][b] = add(mult(mult(4, a), f(a - 1, b - 1)), f(a, b - 1)); 
}

int c(int a, int b) {
	if(a == b || !b) return 1;
	if(C[a][b] != -1) return C[a][b];
	return C[a][b] = add(c(a - 1, b), c(a - 1, b - 1));
}

int main() {
	memset(C, -1, sizeof(C));
	memset(F, -1, sizeof(F));

	scanf("%d%d", &h, &w); 

	int ans = MOD - 1;
	for(int n = 0; n <= w && h >= 2 * n; ++n) {	
		int v = c(w, n); 
		for(int i = 0; i < n; ++i) v = mult(v, c(h - 2 * i, 2)); 

		int prod = 1;
		for(int m = 0; m <= h && h >= 2 * n + m && w >= 2 * m + n; ++m) {	
			ans = add(ans, mult(v, mult(mult(c(h - 2 * n, m), prod), f(w - n - 2 * m, h - 2 * n - m))));
			prod = mult(prod, c(w - n - 2 * m, 2));
		}
	}
	printf("%d\n", ans);
	return 0;
}

Compilation message (stderr)

construction.cpp: In function 'int main()':
construction.cpp:51:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   51 |  scanf("%d%d", &h, &w);
      |  ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 0 / 7
• Subtask 2: 0 / 9
• Subtask 3: 0 / 84