CSES - HIIT Open 2019 - Results
 Task: Bit Strings Sender: Piltit Submission time: 2019-05-25 12:50:26 +0300 Language: C++ Status: READY Result: ACCEPTED
Test results
testverdicttime
#1ACCEPTED0.03 sdetails
#2ACCEPTED0.02 sdetails
#3ACCEPTED0.01 sdetails
#4ACCEPTED0.02 sdetails
#5ACCEPTED0.02 sdetails
#6ACCEPTED0.02 sdetails
#7ACCEPTED0.01 sdetails
#8ACCEPTED0.01 sdetails
#9ACCEPTED0.02 sdetails
#10ACCEPTED0.03 sdetails
#11ACCEPTED0.05 sdetails
#12ACCEPTED0.05 sdetails
#13ACCEPTED0.04 sdetails
#14ACCEPTED0.04 sdetails
#15ACCEPTED0.04 sdetails
#16ACCEPTED0.04 sdetails
#17ACCEPTED0.06 sdetails
#18ACCEPTED0.22 sdetails

### Code

```#include <iostream>

using namespace std;

long long d[1010101];
const long long P = (1e9)+7;

long long modpow(long long b, long long e) {
if (e == 0) return 1%P;
long long u = modpow(b, e/2);
u = (u*u)%P;
if (e%2) u = (u*b)%P;
return u;
}

int main() {
d[0] = 1;
long long n, k;
cin >> n >> k;
for (long long i = 1; i <= n; i++) {
if (i < k) d[i] = modpow(2, i);
else if (i == k) d[i] = (modpow(2, i)-(long long)1)%P;
else d[i] = (d[i-1]*(long long)2 % P - d[i-k-1] % P + P) % P;
}
cout << d[n] << endl;
}

```

### Test details

#### Test 1

Verdict: ACCEPTED

input
1 1

correct output
1

user output
1

#### Test 2

Verdict: ACCEPTED

input
2 1

correct output
1

user output
1

#### Test 3

Verdict: ACCEPTED

input
2 2

correct output
3

user output
3

#### Test 4

Verdict: ACCEPTED

input
3 1

correct output
1

user output
1

#### Test 5

Verdict: ACCEPTED

input
3 2

correct output
5

user output
5

#### Test 6

Verdict: ACCEPTED

input
3 3

correct output
7

user output
7

#### Test 7

Verdict: ACCEPTED

input
4 1

correct output
1

user output
1

#### Test 8

Verdict: ACCEPTED

input
4 2

correct output
8

user output
8

#### Test 9

Verdict: ACCEPTED

input
4 3

correct output
13

user output
13

#### Test 10

Verdict: ACCEPTED

input
4 4

correct output
15

user output
15

#### Test 11

Verdict: ACCEPTED

input
654321 123456

correct output
796245691

user output
796245691

#### Test 12

Verdict: ACCEPTED

input
1000000 1

correct output
1

user output
1

#### Test 13

Verdict: ACCEPTED

input
1000000 10

correct output
256933600

user output
256933600

#### Test 14

Verdict: ACCEPTED

input
1000000 100

correct output
142013415

user output
142013415

#### Test 15

Verdict: ACCEPTED

input
1000000 1000

correct output
899626120

user output
899626120

#### Test 16

Verdict: ACCEPTED

input
1000000 10000

correct output
374265948

user output
374265948

#### Test 17

Verdict: ACCEPTED

input
1000000 100000

correct output
388134512

user output
388134512

#### Test 18

Verdict: ACCEPTED

input
1000000 1000000

correct output
235042058

user output
235042058