HDU 4602

EASY PROBLEM

#include <cstdio>#include <iostream>#include <cstring>using namespace std;typedef long long LL;const int maxn = 111111;const int mod = (int) (1e9 + 7);char s[maxn];int num[maxn];LL POW(LL a, LL b) {    LL ans = 1, t = a;    while (b) {        if (b & 1)            ans = ans * t % mod;        t = t * t % mod;        b >>= 1;    }    return ans;}LL solve(LL n, LL k) {    if (k > n)        return 0;    if (k == n)        return 1;    if (k == n - 1)        return 2;    LL a = POW(2, n - k - 2), b = POW(2, n - k);    LL ans = a * (n - k - 1) + b;    ans = (ans % mod + mod) % mod;    return ans;}int main() {    ios::sync_with_stdio(false);    int T;    cin >> T;    while (T--) {        LL n, k;        cin >> n >> k;        cout << solve(n, k) << endl;    }    return 0;}