Bit Strings

#include <iostream>
#include <map>

using namespace std;

long n, k;
map<pair<long, long>, long> cache;

long add_nr(long zs, long ln) {
    if (ln == n) {
        return 1;
    }
    pair<long, long> t = make_pair(zs, ln);
    if (cache[t] == 0) {
        if (zs != k - 1) cache[t] = add_nr(zs + 1, ln + 1) + add_nr(0, ln + 1)  % 1000000007;
        else cache[t] = add_nr(0, ln + 1) % 1000000007;
    }
    return cache[t];
}

int main()
{
    cin >> n;
    cin >> k;

    cout << add_nr(0, 0) << endl;

    return 0;
}

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: TIME LIMIT EXCEEDED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: TIME LIMIT EXCEEDED

Test 14

Verdict: TIME LIMIT EXCEEDED

Test 15

Verdict: TIME LIMIT EXCEEDED

Test 16

Verdict: TIME LIMIT EXCEEDED

Test 17

Verdict: TIME LIMIT EXCEEDED

Test 18

Verdict: TIME LIMIT EXCEEDED