Check for consecutive numbers

问题

I have an array m of integers. I'm looking for a method to check if the elements of m are consecutive. Is there a way to test for consecutive numbers?

I came up with this code intended to work when the array length is four:

m.count == 4 && (m.max-m.min) == 3

which incorrectly returns true for [1,1,1,4] or [0,0,0,3].

回答1:

Enumerable has a really handy method called each_cons that works like this:

[1,2,3,4].each_cons(2).to_a # => [ [1, 2], [2, 3], [3, 4] ]

That is, it yields each consecutive set of n elements. In our case n is 2.

Of course, as the name implies, it returns an Enumerator, so we can chain it with other Enumerable methods like all?:

def four_consecutive?(arr)
  return false unless arr.size == 4
  arr.each_cons(2).all? {|a, b| b == a + 1 }
end

four_consecutive?([2,3,4,5])   # => true
four_consecutive?([2,2,2,5])   # => false
four_consecutive?([1,2,3,4,5]) # => false

This method has the advantage above others that, because all? short-circuits as soon as the block returns false, it will only test numbers until it finds a pair that don't meet the condition (b == a + 1). Of course, with only four elements this doesn't really make a difference—unless you're calling this method thousands of times in situation where performance matters.

回答2:

You can try this:

a == (a.min..a.max).to_a && a.count == 4

This only works when the array is in increasing order. [3, 4, 5, 6] will pass but [4, 3, 5, 6] won't.

回答3:

The Answer is based on mathematical problem for Sum of consecutive integers

Sum = n∗(n+1)/2

Code:

def check_sum_match?(arr)
  m = arr.min - 1
  n = arr.max
  sum1 = arr.inject{|sum, x| sum = sum + x}
  sum2 = (n*(n+1) - m*(m+1))/2
  sum1 == sum2
end

arr = [5,6,7,8]
if arr.count == 4 && check_sum_match?(arr)
  puts 'Yes condition matches'
else
  puts 'Invalid Array'
end
# valid arrays are
# [4,6,5,7], [4,5,6,7], etc

Tentative Explanation:

回答4:

If a is the array and n is the required size:

def size_and_consecutive?(a, n)
  a == (a.first..(a.first+n-1)).to_a
end

size_and_consecutive? [3,4,5,6], 4
  #=> true
size_and_consecutive? [4,3,5,6], 4
  #=> false
size_and_consecutive? [3,4,5], 4
  #=> false

回答5:

A compact solution that I could come up with is as follows:

def consec(arr)
  is_of_proper_length = (arr.size == 4)
  if(is_of_proper_length)
    are_consec = true
    arr.each_cons(2) {|x,y| are_consec = false unless ((y - x) == 1)}
  end
  is_of_proper_length && are_consec
end

Output:

consec([1,2,3,4])
 => true 
2.2.0 :051 > consec([0,0,0,0])
 => false 
2.2.0 :052 > consec([4,6,5,7])
 => true 
2.2.0 :053 > consec([4,5,6,7])
 => true 
2.2.0 :054 > consec([5,6,7,8])
 => true 
2.2.0 :055 > consec([2,2,2,5])
 => false 
2.2.0 :056 > consec([2,3,4,5])
 => true 
2.2.0 :057 > consec([1,2,3,4,5])
 => false

来源：https://stackoverflow.com/questions/32973830/check-for-consecutive-numbers

标签

arrays

ruby

integer

conditional-statements