test_table1 = {}
for k, v in pairs(test_table) do
  test_table1[v] = true
end
 

test_table1 = {}
for k, v in pairs(test_table) do
  test_table1[v] = true
end
 

test_table={"qwe", "1qweasd", "zxc"}
test_table1={["qwe"]=true, ["1qweasd"]=true, ["zxc"]=true}
str = "1qweasd"

function check1(t, str)
  return (string.find("|"..table.concat(t,"|").."|", "|"..str .. "|") ~=nil)
end

function check2(t, str)
  for k, v in pairs(t) do
    if v == str then return true end
  end
  return false
end

function check3(t, str)
  return (t[str] or false)
end
max_count=1000000
_s=os.clock()
for i=1, max_count do
  res = check1(test_table, str)
end
_e = os.clock()
print("check1 took "..tostring(_e-_s))
_s=os.clock()
for i=1, max_count do
  res = check2(test_table, str)
end
_e = os.clock()
print("check2 took "..tostring(_e-_s))

_s=os.clock()
for i=1, max_count do
  res = check3(test_table1, str)
end
_e = os.clock()
print("check3 took "..tostring(_e-_s))   
--[[ 
check1 took 0.752
check2 took 0.261
check3 took 0.116 
--]]