# Permutations

ashok mandala

Greenhorn

Posts: 9

posted 3 years ago

- 1

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 3 years ago

why not {2,3,1} is good permutation?

- 2

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: 50714

83

posted 3 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 3 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: 50714

83