我复制了算法，用这里的堆栈来做： How to put postfix expressions in a binary tree?
问题是我最终得到了一个节点，但我需要一个二叉树。
String currentPartOfEquation;
Stack<Node<String>> inputProcessor = new Stack(postFixExpression.size()); //create a stack of the size of how many parts there are to the expression. technically, a length of a string.
Iterator<String> lookThroughInput = postFixExpression.iterator();
//iterate through the input!
BinaryTree<String> output = new BinaryTree<String>();
while(lookThroughInput.hasNext()) //Is there something left?
{
currentPartOfEquation = lookThroughInput.next(); //we read next input! We read one symbol of a postfix expression.
if(currentPartOfEquation.equals("*") ||
currentPartOfEquation.equals("/") || currentPartOfEquation.equals("-")
|| currentPartOfEquation.equals("+")) //Do we have a math operator as the symbol read in the expression?
{
//the first extracted off stack will end up being a right child for the current operator....
//we're popping based on an algorithm
//of making leaf nodes for #s following with
//giving 'em families with the operator input found here as a parent.
Node<String> right = inputProcessor.pop();
//operator's children!!!!
Node<String> left = inputProcessor.pop();
// operator node with its family relations. no parent yet, so null for that field
// we are creating a tree every time using the class definition.
Node<String> parent = createNode(currentPartOfEquation, temp, left, right);
temp = parent;
//for a parental connection for each next op to each previous op.
// push this family node into our stack using the class definition.
inputProcessor.push(parent);
}
else //we see a number in our input!!!
{
//no parents or children, just the NUMBER stored in a node!!!!!!! it's our LEAF NODE!!!!
Node<String> leaf = createNode(currentPartOfEquation, null, null, null);
// push this leaf node holding a # into our stack!!!!!
inputProcessor.push(leaf);
}
}
return inputProcessor.top();
// at the end there should be be one element in the stack holding the entire family in correct order!!!!! this tree should be created by the very end.
有关二进制树如何与节点相关的一些信息：
节点实现位置以及它们的连接方式。 node是一个内部类，包含父，左，右（所有节点）和元素（对象）作为实例变量。
Node类中的构造函数指定元素，父元素，左元素，右元素。二进制树包含一个名为root的实例变量Node，它是树的顶层元素 - 根 - 而createNode也是它的功能。
createNode确实返回新节点，并将元素，父，左，右分别对应于Node的构造函数。
通过二叉树的方法（它们都返回位置并从参数中获取位置，但是使用节点），二叉树连接节点（像右边添加，左边添加等）
二进制树中的验证方法经常使用一个位置并将其作为节点返回。