Submission #71721

#	Time	Username	Problem	Language	Result	Execution time	Memory
71721		유애나 (#119)	Cross on the Grid (FXCUP3_cross)	C++98	100 / 100	3 ms	724 KiB

cross

#include <bits/stdc++.h>
using namespace std;

const int M = int(1e9) + 7;

struct Mat{
    int a[9][9];
    Mat operator*(const Mat &o) const {
        Mat r;
        for(int i = 0; i < 9; i++){
            for(int j = 0; j < 9; j++){
                r.a[i][j] = 0;
                for(int k = 0; k < 9; k++)
                    r.a[i][j] = (r.a[i][j] + 1LL * a[i][k] * o.a[k][j]) % M;
            }
        }
        return r;
    }
} a;

Mat p(Mat x, int k){
    if(k == 1) return x;
    if(k & 1) return p(x * x, k / 2) * x;
    return p(x * x, k / 2);
}

int n, r;
int t[9][9] = {
    {1, 0, 0, 0, 1, 0, 1, 1, 0},
    {1, 0, 0, 0, 0, 0, 1, 1, 0},
    {1, 0, 0, 0, 1, 0, 0, 1, 0},
    {1, 0, 0, 0, 1, 0, 1, 0, 0},
    {0, 1, 0, 0, 0, 0, 0, 0, 1},
    {0, 1, 0, 0, 0, 0, 0, 0, 0},
    {0, 0, 1, 0, 0, 0, 0, 0, 0},
    {0, 0, 0, 1, 0, 1, 0, 0, 0},
    {0, 0, 0, 1, 0, 0, 0, 0, 0}
};

int main(){
    scanf("%d", &n);
    if(n == 3){ puts("4"); return 0; }
    for(int i = 0; i < 9; i++) for(int j = 0; j < 9; j++) a.a[i][j] = t[i][j];
    a = p(a, n - 3);
    for(int i = 0; i < 9; i++) for(int j = 0; j < 4; j++) r = (r + a.a[i][j]) % M;
    printf("%d\n", r);
}

Compilation message (stderr)

cross.cpp: In function 'int main()':
cross.cpp:41:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~

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