__builtin __builtin_clz(a) std::hypotl 计算 $(x, y)$ 平方和开平方根 std::hypotl(x, y) list `cpp std::list list; list.push_front(0); std::vector::iterator> it(N); it[0] = list.begin(); for (int i = 1; i < N; i++) { int k, p; std::cin...