qsort in lua

qsort.lua

#!/usr/bin/env lua

function qsort (t, lo, hi)
    if lo > hi then
        return
    end
    local p = lo
    for i=lo+1, hi do
        if (t[i] < t[lo]) then
            p = p + 1
            t[p], t[i] = t[i], t[p]
        end
    end
        t[p], t[lo] = t[lo], t[p]
        qsort(t, lo, p-1)
        qsort(t, p+1, hi)
end

function three_ways_qsort(t, lo, hi)
    if lo >= hi then
        return
    end
    local lt = lo
    local i = lo
    local gt = hi
    local pivot = t[lo]
    while i <= gt do
        if t[i] < pivot then
            t[lt], t[i] = t[i], t[lt]
            lt = lt + 1
            i = i + 1
        elseif t[i] > pivot then
            t[i], t[gt] = t[gt], t[i]
            gt = gt - 1
        else
            i = i + 1
        end
    end
    three_ways_qsort(t, lo, lt-1)
    three_ways_qsort(t, gt+1, hi)
end

--[[
t={3,2,1,5,10,6}
qsort(t, 1, #t)
for i, v in ipairs(t) do
    print(v)
end
--]]

t={5,3,1,3,5,7,6,2,9,7,5,2,8,4,1}
three_ways_qsort(t, 1, #t)
for i, v in ipairs(t) do
    print(v)
end