Friends problems

#1

when n=0 , then we have 1 ways means when no one is going ???

#2

yes bhaiya had told it in video
that if n=0 we have one way which is for the case when no one is going

but it will depend on question it’s there choice whether they include n=0 or say n>0

so check once when you submit the code

i hope this helps
if yes hit a like and don’t forgot to mark doubt as resolved :grinning:
if you have more doubts regarding this feel free to ask

#3

@asaurabh_26 i am trying to solve this problems simply using the fibnaaci concepts,
n == 0 return 0, n == 1 return 1, n == 2 return 2; and f(n-1) + f(n-2); so i am gettting the 3 ways when n=4, so it this right but when i dry the problems it actually 4 ways what to do???

#4

Even i forget some of concepts of permutation and combination…

#5

this recursive relation is not correct
correct one
f(n)= f(n-1) + (n-1)*f(n-2)

use this relation

#6

not much concepts are needed in this question

#7

@asaurabh_26 can explain the second part of the recursion relation do understand it better…

#8

as explained in video

a person has 2 options

  1. it goes alone
    f(n-1)

  2. it goes with friend so first he has to pick a friend
    and to pick a friend he has n-1 option (he can pick any one from n-1 friends except him)
    now n-2 persons left
    so recursive call look like
    (n-1)*f(n-2)

so finally we have
f(n)= f(n-1) + (n-1)*f(n-2)

#9

@asaurabh_26 I got it. Can u explain when they is n == 0 then 1 ways in always exits The same things is apply in the ladder problem but i didn’t get it.
when no one is going to party there is 1 ways?? and also when we stand on the ground in ladder problems we have 1 ways to stand there?? how … Is i am misssing something

#10

in case of friend problem
if n==0 then there is 1 way which is no one goes to party

in case of ladder problem
f(n) is no of ways to stand at nth ladder
if n==0 means we are at ground so there is one way to stand at ground hence return 1

#11

@asaurabh_26 ya bro my doubt is same it means how this is possible when no is going to party then how its 1 ways actually there is 0 ways…

#12

how is that 0 ways ??

no one is going
so it should be counted as 1 way

for a work you have two options
either you do it or not

you can’t say i have only one option
i can do this
if don’t do it then this is not a way

#13

i hope this helps

don’t forgot to mark doubt as resolved :grinning:
if you have more doubts regarding this feel free to ask

#14

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