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