Lua 学习笔记（十）数据结构

--双向队列的实现

DoubleQueue = {}

function DoubleQueue.new()
     local Queue = { first = 0, last = -1 }
     function Queue.pushFirst( queue,value )
          local first = queue.first -1
          queue.first = first
          queue[ first ] = value
     end

     function Queue.popFirst( queue )
          local first = queue.first
          if first > queue.last then error(" queue is empty! ") end
          local value = queue[first]
          queue[first] = nil
          queue.first = first +1
          return value
     end

     function Queue.pushLast( queue,value )
          local last = queue.last +1
          queue.last = last
          queue[last] = value
     end

     function Queue.popLast( queue )
          local last = queue.last
          if last < queue.first then error( " queue is empty! " ) end
          local value = queue[last]
          queue[last] = nil
          queue.last = last -1
          return value
     end

     function Queue.len( queue )
          return queue.last - queue.first +1
     end
     return Queue
end