Method fast_pow

343. Integer Break/Solution.cpp:29–36

    }

    int fast_pow(int x, int y) {
        int res = 1;
        for (int offset = sizeof(int) * 8 - 1; offset >= 0; offset --) {
            res *= res;
            if (y & (1 << offset)) res *= x;
        } 
        return res;
    }

};