逆波兰表达式生成算法是比较当前运算符与栈顶运算符的优先关系，若当前运算符的优先级高于栈顶运算符，则当前运算符入栈，若当前运算符的优先级低于栈顶运算符，则栈顶运算符退栈。-Reverse Polish expression generation algorithm is more current operator and the operator stack ranking, if the current operator precedence than the stack operator, t