通过使用多级队列对表达式中的字符串进行优先级的排列，从而实现表达式的计算。比课本中的算法要好很多，可以满足无限制优先级排列的要求。-Through the use of multi-level queue of expression in the string with priority in order to achieve the calculation of expression. Than textbooks, many of the algorithm is better able t