moistx https://blog.hatena.ne.jp/moistx/ Logfiles https://logfiles.hatenablog.com/ SRM 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); } }; 190 <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> Hatena Blog https://hatena.blog 2014-08-17 08:08:58 rich https://logfiles.hatenablog.com/entry/20140817/1408230538 1.0 100%