such type of question anyone can do by using trandational approch
but there is a quick way to do this.
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just take anyone router in our case assume R1 now try to go from this router to every other router
and try to list all used link and unused link
when we will go from R1—to all remaning link then used link are(here cost are diffrent so i will only do numering for used and unused link)
R1 used =3 2 7 9 4
and unused link are :-1 6 8
now what we will do here now we will focus only on unused link that R1 not used
we will try to see it is possible remaning node can used thes path.
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so ,here now if you will send from R5 -R6 then 1 will used now we are left with only 8 and 6
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now focus on 8 what what does it says if you are at R4 so you can go to R6 by using 8 cost or you can also go to R5 via R6 with cost of 8+4 but you ask yourself is it minimum.
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now if you are at R5 then you can go to R6 with cost 5 which is better then 8 and if you are at R4 also you can go to R6 with cost 4 which is definetly better than 1+8.
so from here we can say 8 is never going to used.in same way at 6 you can apply this technique and you can make sure this link also never going to used
