写一下二叉树  推一下公式就出来了， 注意取模时的输出形式

#include 
     
      #define mem(a, b) memset(a, b, sizeof(a))using namespace std;typedef long long LL;const int maxn = 1e6+5, INF = 0x7fffffff, MOD = 1e9+7;LL n, k;LL qp(LL a, LL b){    LL res = 1;    while(b)    {        if(b & 1) res = res * a % MOD;        a = a * a % MOD;        b >>= 1;    }    return res;}int main(){    while(cin>> n >> k)    {        if(n == 0)        {            cout<< 0 <