判断一个逻辑表达式是否是重言式，用户输入正确的逻辑表达式，计算机按照运算优先顺序生成二叉树，再用后序遍历得到逆波兰表达式，用逆波兰表达式来判断输入的表达式是否是重言式，用户也可以自己赋值来测试表达式的真假！-Determine whether a logical expression is a tautology, users enter the correct logical expression, the computer generates a binary tree in accordance with operational priorities, and then be against Poland after traversing the expression, using reverse Polish expressions to determine the expression of input type it is a tautology, users can assign to test your expression of true and false!