25 - Range Extraction

Don’t say so much, just coding…

Instruction

A format for expressing an ordered list of integers is to use a comma separated list of either

• individual integers
• or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, ‘-‘. The range includes all integers in the interval including both endpoints. It is not considered a range unless it spans at least 3 numbers. For example (“12, 13, 15-17”)

Complete the solution so that it takes a list of integers in increasing order and returns a correctly formatted string in the range format.

Example:

  solution([-6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20])
  # returns "-6,-3-1,3-5,7-11,14,15,17-20"
``  

### Ruby

#### Init

```ruby
  def solution(list)
    #todo: complete solution
  end

Sample Testing

Test.assert_equals(solution([-6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20]), "-6,-3-1,3-5,7-11,14,15,17-20")

Javascript

Init

function solution(list){
 //TODO: complete solution 
}

Sample Testing

Test.assertEquals(solution([-6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20]), "-6,-3-1,3-5,7-11,14,15,17-20")

---

Thinking

想法(1): 如果現在的數 +1 跟下一位數相等，就會被算在同個區間
想法(2): 如果只有一位數的話回傳該數，一位到兩位數之間回傳該兩位數，超過則回傳區間並且加上符號 -

圖片來源：Unsplash Sincerely Media

Hint & Reference

• Ruby
  • Ruby - apidock chunk_while
  • Ruby - apidock flat_map
• JavaScript
  • JS - MDN Array.prototype.splice()

Solution

Ruby

# Solution 1
def solution(list)
  list.chunk_while { |i, j| i + 1 == j }
      .flat_map { |a|
        if a.size == 1
          a.first.to_s
        elsif a.size == 2 
          [a.first.to_s, a.last.to_s]
        else
          "#{a.first}-#{a.last}"
        end
      }
      .join(',')
end

Javascript

// Solution 1
function solution(list){
   for(var i = 0; i < list.length; i++){
      var j = i;
      while(list[j] - list[j + 1] == -1) j++;
      if(j != i && j-i > 1) list.splice(i, j - i+1, list[i] + '-' + list[j]);
  }
  return list.join();
}