.. index:: 吸氧

编译优化
========

    ``#pragma GCC optimize(0)`` -> 
    
    ``#pragma GCC optimize(3)`` -> 
    
    ``#pragma GCC optimize(3, "inline")``

    ``5.2s`` -> ``1.8s`` -> ``1.0s``

    吸氧大法好 ``QAQ`` 。

    .. code-block:: CPP

        #pragma GCC optimize(3, "inline")
        #include <bits/stdc++.h>

        using i64 = long long;
        using u64 = unsigned long long;

        u64 f(int u) {
            if (u == 1)
                return 1ULL;
            else if (u == 2)
                return 1ULL;
            else {
                return f(u - 2) + f(u - 1);
            }
        }

        int main() {
            std::cout << f(45) << '\n' << ((double)clock() / CLOCKS_PER_SEC) << "s\n";
            return 0;
        }