34 lines
1.0 KiB
Lua
34 lines
1.0 KiB
Lua
function partition (list, left, right, pivotIndex)
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local pivotValue = list[pivotIndex]
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list[pivotIndex], list[right] = list[right], list[pivotIndex]
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local storeIndex = left
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for i = left, right do
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if list[i] < pivotValue then
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list[storeIndex], list[i] = list[i], list[storeIndex]
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storeIndex = storeIndex + 1
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end
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end
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list[right], list[storeIndex] = list[storeIndex], list[right]
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return storeIndex
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end
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function quickSelect (list, left, right, n)
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local pivotIndex
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while 1 do
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if left == right then return list[left] end
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pivotIndex = math.random(left, right)
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pivotIndex = partition(list, left, right, pivotIndex)
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if n == pivotIndex then
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return list[n]
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elseif n < pivotIndex then
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right = pivotIndex - 1
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else
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left = pivotIndex + 1
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end
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end
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end
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math.randomseed(os.time())
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local vec = {9, 8, 7, 6, 5, 0, 1, 2, 3, 4}
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for i = 1, 10 do print(i, quickSelect(vec, 1, #vec, i) .. " ") end
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