# Project Euler #222: Sphere Packing

# Project Euler #222: Sphere Packing

+ 4 comments Hi ,

For the third test case I'm getting 533543 . i did it on papers as well still the answer is 533543. Here is my answer details:

Balls are arranged in descending order. Distance between centre of : a) 1st ball and 2nd ball = 107.703 b) 2nd and 3rd ball = 103.923 c) 3rd and 4th ball = 100 d) 4th and 5th ball = 95.917

total distance between centre of 1st ball (radius 65) to last ball (radius 61) = 407.543

adding the radius of 1st and last ball to get the min. height of pipe = 407.543 + 65 + 61 = 533.543

Answer : 533543.

Could you please let me know where i am going wrong . I feel my answer is correct

+ 2 comments How do you manage rounding errors in a sum of 10^5 square roots?

Edit : I used the Kahan summation algorithm with success

+ 1 comment Hi. This is my GO solution below, but it doesn't pass the test cases from 3 to last.

It's surely correct the way culculation I think, so I'm confused about it.

What is wrong with this solution? Significant figure??

package main import ( "bufio" "fmt" "math" "os" "sort" "strconv" ) func nextInt() int { sc.Scan() i, e := strconv.Atoi(sc.Text()) if e != nil { panic(e) } return i } func swap(array []int) []int { var newArray []int for i := range array { if i % 2 == 0 { newArray = append(newArray, array[i]) } } sort.Ints(array) // array2を昇順に for i := range array { if len(array) % 2 == 0 { if i % 2 == 0 { newArray = append(newArray, array[i]) } } else { if i % 2 == 1 { newArray = append(newArray, array[i]) } } } return newArray } var sc = bufio.NewScanner(os.Stdin) func main() { sc.Split(bufio.ScanWords) r, n := nextInt(), nextInt() var radii[]int for i := 0; i < n; i ++ { radii = append(radii, nextInt()) } sort.Sort(sort.Reverse(sort.IntSlice(radii))) // radiiを降順に if n == 1 { fmt.Println(r * 2000) } else if n == 2 { isDistance := math.Sqrt(float64(4 * r * (radii[0] + radii[1] - r))) otherRadii := float64(radii[0] + radii[1]) ans := (isDistance + otherRadii) * 1000 fmt.Println(math.Floor(ans + .5)) } else { newArray := swap(radii) var isTotalDistance float64 for i := 0; i < len(newArray) - 1; i++ { isTotalDistance += math.Sqrt(float64(4 * r * (newArray[i] + newArray[i + 1] - r))) } otherRadii := float64(newArray[0] + newArray[len(newArray) - 1]) ans := (isTotalDistance + otherRadii) * 1000 fmt.Println(math.Floor(ans + .5)) } }

+ 0 comments can some one please explain the question? I am unable to understand what exactly the question refers to

+ 1 comment hi can anyone please tell me what's wrong with this code cause it's not working after test case 2 import math

import math R,n = map(int,input().split()) r = list(map(int,input().split())) dist = [] for i in range(n): if i!=n-1: d = r[i]+r[i+1] x = 2*R - d y = math.sqrt(d*d-x*x) dist.append(y) height = sum(dist)+r[0]+r[len(r)-1] print(round(height*1000))

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