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  1. # @file pendulum.002.rb
  2. # Question-8 from some problem set.
  3. # @date 03/28/2026
  4.  
  5. # Rearrange the word so the character with the smallest ASCII value
  6. # is placed at the center, the second smallest to its right and the
  7. # third to its left and so on.
  8. #
  9. # Example-1: In : COMPUTER
  10. #            Out: TPMCEORU
  11. #
  12. # Example-2: In : SCIENCE
  13. #            Out: SIECCEN
  14. #
  15. # The problem specifies characters should be rearranged by invoking
  16. # the function 'int minimumCharIndex(String str)'.
  17.  
  18. def minimum_char_index(s)
  19.   s.index(s.each_byte.min.chr) # faster than each_char.min
  20. end
  21.  
  22. def pendulum_0(s)
  23.   s = s.dup
  24.   n = s.size
  25.   m = (n-1) / 2
  26.   r = []
  27.   n.times do |i|
  28.     k = minimum_char_index(s)
  29.     m = i.even? ? m-i : m+i
  30.     r[m] = s.slice!(k)
  31.   end
  32.   r.join
  33. end
  34.  
  35. # Breaking the rules a bit.
  36.  
  37. def minimum_index(a, first, last)
  38.   subarray = a[first...last]
  39.   subarray.index(subarray.min) + first
  40. end
  41.  
  42. def pendulum_0_1(s)
  43.   s = s.bytes
  44.   n = s.size
  45.   m = (n-1) / 2
  46.   r = []
  47.   n.times do |i|
  48.     k = minimum_index(s, i, n)
  49.     m = i.even? ? m-i : m+i
  50.     r[m] = s[k]
  51.     s[k] = s[i]
  52.   end
  53.   r.map(&:chr).join
  54. end
  55.  
  56. def swap!(a, i, j)
  57.   a[i], a[j] = a[j], a[i] if i != j
  58.   a
  59. end
  60.  
  61. def selectsort!(a)
  62.   (a.size-1).times do |i|
  63.     swap!(a, i, minimum_index(a, i, a.size))
  64.   end
  65.   a
  66. end
  67.  
  68. def pendulum_0_2(s)
  69.   n = s.size
  70.   m = (n-1) / 2
  71.   r = []
  72.   selectsort!(s.bytes).each_with_index do |x, i|
  73.     r[m = i.even? ? m-i : m+i] = x
  74.   end
  75.   r.map(&:chr).join
  76. end
  77.  
  78. # Breaking the rules a bit more.
  79.  
  80. def pendulum_1(s)
  81.   n = s.size
  82.   m = (n-1) / 2
  83.   r = []
  84.   s.chars.sort!.each_with_index do |x, i|
  85.     r[m = i.even? ? m-i : m+i] = x
  86.   end
  87.   r.join
  88. end
  89.  
  90. def pendulum_2(s)
  91.   r = []
  92.   s.chars.sort!.each_with_index do |x, i|
  93.     r.public_send(i.even? ? :unshift : :push, x)
  94.   end
  95.   r.join
  96. end
  97.  
  98. def pendulum_3(s)
  99.   t = s.chars.sort!
  100.   l, r = t.drop(1).partition.each_with_index{|_, i| i.odd?}
  101.   (l.reverse + t.take(1) + r).join
  102. end
  103.  
  104. def pendulum_4(s)
  105.   l, r = (1...s.size).partition{|i| i.even?}
  106.   s.chars.sort!.values_at(*l.reverse, 0, *r).join
  107. end
  108.  
  109. # Main.
  110.  
  111. def test(f)
  112.   ss = ["", "a", "ba", "bca", "computer", "science"]
  113.   rs = ["", "a", "ab", "cab", "tpmceoru", "sieccen"]
  114.  
  115.   ss.zip(rs) do |s, r|
  116.     s = f.call(s)
  117.     if s != r
  118.       puts ".Failed: expected `#{r}' got `#{s}'"
  119.       return
  120.     end
  121.   end
  122.   puts ".Passed"
  123. end
  124.  
  125. def time(f)
  126.   def choices(pool, n)
  127.     n.times.map{pool.sample}
  128.   end
  129.  
  130.   symbols = ('a'..'z').to_a
  131.   elapsed = 0
  132.  
  133.   12.times do |i|
  134.     s = choices(symbols, 2**i).join
  135.     t = Time.now
  136.     f.call(s)
  137.     elapsed += Time.now - t
  138.   end
  139.   printf(".Elapsed: %.6fs\n", elapsed)
  140. end
  141.  
  142. fs = [
  143.   :pendulum_0,
  144.   :pendulum_0_1,
  145.   :pendulum_0_2,
  146.   :pendulum_1,
  147.   :pendulum_2,
  148.   :pendulum_3,
  149.   :pendulum_4
  150. ]
  151.  
  152. fs.map(&method(:method)).each do |f|
  153.   puts f.name
  154.   test(f)
  155.   time(f)
  156. end
Success #stdin #stdout 0.2s 37456KB
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pendulum_0
.Passed
.Elapsed: 0.097306s
pendulum_0_1
.Passed
.Elapsed: 0.044082s
pendulum_0_2
.Passed
.Elapsed: 0.036619s
pendulum_1
.Passed
.Elapsed: 0.002647s
pendulum_2
.Passed
.Elapsed: 0.001967s
pendulum_3
.Passed
.Elapsed: 0.002730s
pendulum_4
.Passed
.Elapsed: 0.002822s
https://ideone.com/Q4PXOd
language:
Ruby (ruby 2.5.5)
created:
2 days ago
visibility:
public

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