How to construct Tetris configurations

Given some Tetris configuration, find a proper sequence of Tetris pieces that generates it ...
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Use the mouse to make a configuration consisting of blue "pixels" (or squares) in the right part of the picture below. The New button clears your configuration. Its height has to be at most 10. The rows until the first empty one from below will be reconstructed. Use the scrollbar to control the width of the game board: between 5 en 14. Note that for game boards of even width some configurations are not constructible!
Use the Step and +/- buttons to stepwise construct the configuration in the left part of the picture below. Falling squares are red, once fixed they turn green, and become sometimes even blue — if they belong to the configuration under construction. The Reset button starts the reconstruction again. The Run button generates the whole sequence — this may take quite some time! For instance, four pixels in a row or column can be easily made with one piece, but the current generic construction uses many more ...

Make sure your browser is Java-enabled. The program has been compiled for 1.1 Java Virtual Machines, so it should run for most versions of most (older) browsers. Unfortunately, newer Chrome versions fail ...

This JavaScript version should work (many thanks to Nouri Khalass) on most machines.

The target configuration is constructed row by row, from below. First a so-called platform is built on top of the previous row, using some extra intermediate rows; this platform fills an entire row — except for one pixel. Then six auxiliary rows are constructed on top of the platform, where the next row of the target configuration sticks out. Platform and auxiliary rows are then cleared, and the construction continues with yet another platform, and so on. After the target configuration has been completed, sometimes some final pixels must be cleared.

Questions/remarks: (Hendrik Jan Hoogeboom and Walter Kosters).

14 January 2016 —