Permutations
ashok mandala
Greenhorn
Posts: 9
posted 4 years ago
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hi frnds i need help for the below problem
consider a permutation of first 'N' natural numbers 'good' if it doesn't have 'x' and 'x+1' appearing consecutively,
where (1 <= x <= N).
for example, for N=3, all 'good' permutations are:
1. {1,3,2}
2. {2,1,3}
3. {3,2,1}
Write a java program that takes an input 'N' and displays the number of possible 'good' permutations. So, for input
of 3 for 'n' above, we would print '3' as the output.
consider a permutation of first 'N' natural numbers 'good' if it doesn't have 'x' and 'x+1' appearing consecutively,
where (1 <= x <= N).
for example, for N=3, all 'good' permutations are:
1. {1,3,2}
2. {2,1,3}
3. {3,2,1}
Write a java program that takes an input 'N' and displays the number of possible 'good' permutations. So, for input
of 3 for 'n' above, we would print '3' as the output.
posted 4 years ago
why not {2,3,1} is good permutation?
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ashok mandala wrote:hi frnds i need help for the below problem
consider a permutation of first 'N' natural numbers 'good' if it doesn't have 'x' and 'x+1' appearing consecutively,
where (1 <= x <= N).
for example, for N=3, all 'good' permutations are:
1. {1,3,2}
2. {2,1,3}
3. {3,2,1}
Write a java program that takes an input 'N' and displays the number of possible 'good' permutations. So, for input
of 3 for 'n' above, we would print '3' as the output.
why not {2,3,1} is good permutation?
~Suresh
ashok mandala
Greenhorn
Posts: 9
Campbell Ritchie
Sheriff
Posts: 54034
130
posted 4 years ago
Welcome to the Ranch 
Read Suresh Sajja’s post carefully; it contains good advice. I would suggest you filter each permutation before adding it to your list, however.
Please don’t use {} around your numbers, because that denotes a set. Use [] for a sequence. So [1, 2, 3] is a “bad” sequence and [3, 2, 1] is a “good” sequence.
Read Suresh Sajja’s post carefully; it contains good advice. I would suggest you filter each permutation before adding it to your list, however.
Please don’t use {} around your numbers, because that denotes a set. Use [] for a sequence. So [1, 2, 3] is a “bad” sequence and [3, 2, 1] is a “good” sequence.
ashok mandala
Greenhorn
Posts: 9
posted 4 years ago
How do YOU, personally, decide if a sequence is valid or not? Let's say I gave you this:
[2,5,3,4,1]
Is that 'good', or 'bad'? How do you know? can you write down the steps that an 8-year old child could follow to determine this?
The most important part of writing code does not involve your computer, but your brain + pencil + paper.
ashok mandala wrote:i got the logic for first step...
but dont know how to filter.....
help me out..........
How do YOU, personally, decide if a sequence is valid or not? Let's say I gave you this:
[2,5,3,4,1]
Is that 'good', or 'bad'? How do you know? can you write down the steps that an 8-year old child could follow to determine this?
The most important part of writing code does not involve your computer, but your brain + pencil + paper.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
mohammed irfan
Greenhorn
Posts: 2
Campbell Ritchie
Sheriff
Posts: 54034
130
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