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A comment on Show HN: Astro-Bot – A programming question with every new tab.

Re:Show HN: Astro-Bot – A programming question with every ne... by seg12 on Tuesday October 30, 2018 @05:29PM (#18341438)
The following is incorrect for finding a missing number in a sequence.

  func foo( _ nums: [Int] ) -> Int {
    var sum = 0
    var _ = nums.map {sum += $0}

    return (nums.count * ((nums.count+1) / 2)) - sum
  }
The last line should be

  return ((nums.count+1) * ((nums.count+2) / 2)) - sum
The count of nums will give the incorrect answer since it's already missing a value.
[ Parent | on HN ]
Re:Show HN: Astro-Bot – A programming question with every ne... by hadeon on Tuesday October 30, 2018 @09:31PM (#18342688)
You're absolutely right, thanks for noticing this. There was also a bug with the parentheses I hadn't caught.
[ Parent | on HN ]