{"version":"1.0","description":"class TheLuckyNumbers { private: int solve(long long n, int a, int b) { if(n > b) return 0; return solve(10*n+4, a, b) + solve(10*n+7, a, b) + (a<=n&&n<=b); } public: int count(int a, int b) { return solve(0, a, b); } };","provider_url":"https://hatena.blog","width":"100%","html":"<iframe src=\"https://hatenablog-parts.com/embed?url=https%3A%2F%2Flogfiles.hatenablog.com%2Fentry%2F20140817%2F1408230538\" title=\"SRM403 Div1Easy TheLuckyNumbers - Logfiles\" class=\"embed-card embed-blogcard\" scrolling=\"no\" frameborder=\"0\" style=\"display: block; width: 100%; height: 190px; max-width: 500px; margin: 10px 0px;\"></iframe>","image_url":null,"type":"rich","author_url":"https://blog.hatena.ne.jp/moistx/","categories":["SRM"],"published":"2014-08-17 08:08:58","author_name":"moistx","height":"190","provider_name":"Hatena Blog","title":"SRM403 Div1Easy TheLuckyNumbers","blog_title":"Logfiles","url":"https://logfiles.hatenablog.com/entry/20140817/1408230538","blog_url":"https://logfiles.hatenablog.com/"}