### কনসেপ্ট

First, you should read the code two times without comment.

I think, you will understand the algorithm. if not, then follow comments.

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Here, we use primary school math logic. let two numbers $1133$ and $333$.

$1133$

$333$

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3399 ->3399 ….. res[0] = 9

33990 ->3738[9] // add 3399 + 33990 = 37389 ….. res[1] = 8

339900 ->3772[8][9] // add 37389 + 339900 = 377289 … res[2] = 2

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377289

on first line we took $3$ and multiply with $1133$ and result is $3399$

on second line we took $3$ and multiply with $1133$, and we got 33990,

then we add this $33990$ with $3399$ and result is $3738[9]$.

on third line, we follow same way.

you should read code first to know `res[0], res[1], res[2]`

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