Submission #62608

#	Time	Username	Problem	Language	Result	Execution time	Memory
62608		imsifile	Cross on the Grid (FXCUP3_cross)	C++14	100 / 100	3 ms	540 KiB

cross

#include<stdio.h>
#include<memory.h>

typedef long long lld;
const lld mod = 1000000007;

struct mat {
	lld ba[9][9];
	mat operator* (const mat &c){
		mat res; memset(res.ba, 0, sizeof(res.ba));
		for(int i=0; i<9; i++){
			for(int j=0; j<9; j++){
				for(int k=0; k<9; k++) res.ba[i][j] += ba[i][k]*c.ba[k][j];
				res.ba[i][j] %= mod;
			}
		}
		return res;
	}
} base, res;

int N;

int main(){
	scanf("%d", &N); N-=4;
	if(N<0){ puts("4"); return 0; }
	memset(base.ba, 0, sizeof(base.ba));
	memset(res.ba, 0, sizeof(res.ba));
	for(int i=0; i<9; i++) res.ba[i][i] = 1;
	base.ba[0][0] = base.ba[0][1] = base.ba[0][2] = base.ba[0][3] = 1;
	base.ba[1][4] = base.ba[1][5] = base.ba[2][6] = base.ba[3][7] = base.ba[3][8] = 1;
	base.ba[4][0] = base.ba[4][2] = base.ba[4][3] = 1;
	base.ba[6][0] = base.ba[6][1] = base.ba[6][3] = 1;
	base.ba[7][0] = base.ba[7][1] = base.ba[7][2] = 1;
	base.ba[5][7] = base.ba[8][4] = 1;

	for(; N; N>>=1){
		if(N&1) res = res*base;
		base = base*base;
	}

	lld sum=0;
	for(int i=0; i<9; i++){
		for(int j=0; j<9; j++) sum += res.ba[i][j];
	}
	printf("%lld\n", sum%mod);
	return 0;
}

Compilation message (stderr)

cross.cpp: In function 'int main()':
cross.cpp:24:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &N); N-=4;
  ~~~~~^~~~~~~~~~

• Subtask 1: 22 / 22
• Subtask 2: 35 / 35
• Subtask 3: 43 / 43