46 lines
807 B
Ruby
46 lines
807 B
Ruby
# Find the k-th smallest value in the array,
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# see test/find_kth_test.rb
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class FindKth
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def initialize(array)
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@array = array
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end
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def find(k)
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raise 'out of bounds' if k >= @array.size
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array = @array.dup
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lo = 0
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hi = array.length - 1
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while lo < hi
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j = partition(array, lo, hi)
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if j < k
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lo = j + 1
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elsif j > k
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hi = j - 1
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else
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return array[k]
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end
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end
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return array[k]
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end
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private
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def partition(array, lo, hi)
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pivot = array[lo]
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i = lo + 1
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j = hi
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loop do
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i += 1 while (i != hi) && (pivot > array[i])
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j -= 1 while (j != lo) && (pivot < array[j])
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break if i >= j
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array[i], array[j] = array[j], array[i]
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end
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array[lo], array[j] = array[j], array[lo]
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j
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end
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end
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