Wherre are the adjacent characters in the title? [3, 4]!
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T`L`:`(.)\1+
:
$.`¶
T`L


Outputs a linefeed-separated list of indices.

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Explanation

T`L`:`(.)\1+


Transliterate runs of the same character into colons, to mark positions where there are duplicate characters.

:
$.`¶


Then replace each colon with the length of the text before it, followed by a linefeed.

T`L


Finally, delete any remaining letters.