python/TangDou/Topic/ksc.cpp

#include <iostream>
using namespace std;
typedef long long LL;
const int mod = 1e9 + 7;
/*
测试用例:
10000000 10000000

答案：
999300007
*/
//快速乘，计算a*b%mod
LL ksc(LL a, LL b) {
    LL ans = 0;
    a %= mod;
    while (b) {
        if (b & 1) ans = (ans + a) % mod;
        b >>= 1; //位运算，右移1位，相当于除以2
        a = (a + a) % mod;
    }
    return ans;
}
int main() {
    LL a, b;
    cin >> a >> b;
    printf("%lld\n", ksc(a, b));
    return 0;
}