<!--info-header-start--><h1>Run-length encoding <img src="https://img.shields.io/badge/-hard-de3d37" alt="hard"/> </h1><blockquote><p>by Hen Hedymdeith <a href="https://github.com/alfaproxima" target="_blank">@alfaproxima</a></p></blockquote><p><a href="https://tsch.js.org/14188/play" target="_blank"><img src="https://img.shields.io/badge/-Take%20the%20Challenge-3178c6?logo=typescript&logoColor=white" alt="Take the Challenge"/></a> </p><!--info-header-end-->

Given a `string` sequence of a letters f.e. `AAABCCXXXXXXY`. Return run-length encoded string `3AB2C6XY`.
Also make a decoder for that string.


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