Bit Strings

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

ll M = 1e9 + 7;

ll pot[1010101];
ll dp[1010101];


int main() {
  ll n,k;
  cin >> n >> k;
  
  pot[0] = 1;
  for (int i = 1; i <= n; i++) {
      pot[i] = pot[i-1]*2;
      pot[i] = pot[i] % M;
  }
  
   for (int i = 0; i < k; i++) {
        dp[i] = pot[i];
   }
   dp[k] = pot[k]-1;
   for (int i = k+1; i <= n; i++) {
        dp[i] += dp[i-1];
        dp[i] += dp[i-1]- dp[i-k-1];
        dp[i] += M;
        dp[i] = dp[i] % M;
    }

    cout << dp[n] << endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED