创建二进制防爆pression树 [英] Build Binary Expression Tree

问题描述

有人能解释如何构建一个二进制EX pression树。

例如我有一个字符串 2 *（1+（2 * 1））; 如何转换这种成二进制EX pression树

  *
 | \
 | \
 2 +
    | \
    1 *
      | \
      2 1
 

解决方案

序转换为preorder或后序

后序输入是：B + C D E + **

1. 在考虑第一个字符，如果它不是符号然后创建节点添加到堆栈
2. 如果字符是符号然后创建节点符号的流行元素，并添加到左和符号的正确
3. 在堆栈推送符号节点。
4. 重复1，2和3，直到迭代器有没有更多的元素

Java实现

 公共Tree.TreeNode createEx pressionTree（）{
    迭代器＆LT;性格＆GT; ITR = postOrder.iterator（）;
    树树=新树（）;
    NodeStack nodeStack =新NodeStack（）;
    Tree.TreeNode节点;
    而（itr.hasNext（））{
        字符c = itr.next（）;
        如果（！ISDIGIT（c））的{
            节点= tree.createNode（C）;
            node.right = nodeStack.pop（）;
            node.left = nodeStack.pop（）;
            nodeStack.push（节点）;
        }其他{
            节点= tree.creteNode（C）;
            nodeStack.push（节点）;
        }
    }
    节点= nodeStack.pop（）;
    返回节点;
}
 

更多信息： http://en.wikipedia.org/wiki/Binary_ex$p $ pssion_tree

Could someone explain how to build a binary expression tree.

For example I have a string 2*(1+(2*1)); How to convert this into a binary expression tree.

 *
 | \
 |  \
 2  +
    |\
    1 *
      |\
      2 1

解决方案

Convert inorder to preorder or postorder

The Postorder input is: a b + c d e +**

1. Consider first character if it is not symbol then create node add it to stack
2. If character is symbol then create node with symbol pop elements and add to left and right of symbol
3. Push symbol node in to the stack.
4. Repeat 1, 2 and 3 till iterator has no more elements

Java Implementation

public Tree.TreeNode createExpressionTree(){
    Iterator<Character>itr = postOrder.iterator();
    Tree tree = new Tree();
    NodeStack nodeStack = new NodeStack();
    Tree.TreeNode node;
    while (itr.hasNext()) {
        Character c = itr.next();
        if(!isDigit(c)){
            node = tree.createNode(c);
            node.right = nodeStack.pop();
            node.left = nodeStack.pop();
            nodeStack.push(node);
        }else{
            node = tree.creteNode(c);
            nodeStack.push(node);
        }
    }
    node = nodeStack.pop();
    return node;
}

More info: http://en.wikipedia.org/wiki/Binary_expression_tree

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