https://medium.com/@highsunday0630/leetcode-c-%E5%88%B7%E9%A1%8C-%E5%B8%B8%E7%94%A8-stl-%E8%AA%9E%E6%B3%95%E9%80%9F%E6%9F%A5%E8%A1%A8-6da457d2940d