我正在尝试使用 Java 从通过管道传输到 System.in 的字符串输入构建二叉树。每当在字符串中遇到来自 az 的字母时，我都会创建一个内部节点（有 2 个子节点）。每当在字符串中遇到 0 时，我都会创建一个外部节点（叶子）。该字符串是预先订购的，所以作为一个例子，如果我有一个输入，例如：
abcd000e000
我应该制作以下二叉树
a / \ b 0 / \ c e / \ / \ d 00 0 / \ 0 0
至少这是我认为我应该根据作业详细信息（在下面的链接中）所做的。我们还获得了整个程序的示例输入和输出：
输入
a0
0 a00
ab000
输出
树 1：
无效！
树 2：
高度：-1
路径长度：0
完成：是
后排序：
树 3：
高度：0
路径长度：0
完成：是
后排序：a
树 4：
高度：1
路径长度：1
完成：是
后排序：ba
我正在尝试使用 Java 实现一个可以为我执行此操作的程序，但我认为我没有正确地制作二叉树。我已经提供了到目前为止我提出的代码，并在每种方法上方的注释中详细说明了到目前为止我在调试时遇到了什么麻烦。如果需要更多上下文，以下链接详细说明了整个分配以及最终目标应该是什么（构建二叉树只是第一步，但我坚持下去）：
import java.io.*;
// Node
class TreeNode {
char value;
TreeNode left;
TreeNode right;
}
// Main class
public class btsmall {
// Global variables
char[] preorder = new char[1000];
int i = 0;
// Main method runs gatherOutput
public static void main(String[] args) throws IOException {
new btsmall().gatherOutput();
}
// This takes tree as input from the gatherOutput method
// and whenever a 0 is encountered in the preorder character array
// (from a string from System.in) a new external node is created with
// a value of 0. Whenever a letter is encountered in the character
// array, a new internal node is created with that letter as the value.
//
// When I debug through this method, the tree "appears" to be made
// as expected as the tree.value is the correct value, though I
// can't check the tree.left or tree.right values while debugging
// as the tree variable seems to get replaced each time the condition
// checks restart.
public void createTree(TreeNode tree) throws IOException {
// Check that index is not out of bounds first
if (i >= preorder.length) {
i++;
} else if (preorder[i] == '0') {
tree = new TreeNode();
tree.value = '0';
tree.left = tree.right = null;
i++;
} else {
tree = new TreeNode();
tree.value = preorder[i];
i++;
createTree(tree.left);
createTree(tree.right);
}
}
// Supposed to print out contents of the created binary trees.
// Intended only to test that the binary tree from createTree()
// method is actually being created properly.
public void preorderTraversal(TreeNode tree) {
if (tree != null) {
System.out.println(tree.value + " ");
preorderTraversal(tree.left);
preorderTraversal(tree.right);
}
}
// Reads System.in for the Strings used in making the binary tree
// and is supposed to make a different binary tree for every line of input
//
// While debugging after the createTree method runs, the resulting tree variable
// has values of tree.left = null, tree.right = null, and tree.value has no value
// (it's just a blank space).
//
// This results in preorderTraversal printing out a single square (or maybe the square
// is some character that my computer can't display) to System.out instead of all
// the tree values like it's supposed to...
public void gatherOutput() throws IOException {
InputStreamReader input = new InputStreamReader(System.in);
BufferedReader reader = new BufferedReader(input);
String line = null;
TreeNode tree = new TreeNode();
while ((line = reader.readLine()) != null) {
preorder = line.toCharArray();
createTree(tree);
preorderTraversal(tree);
i = 0;
}
}
}
谁能帮助我正确构建二叉树并指出我做错了什么会导致我目前得到的输出？我至少在正确的轨道上吗？有什么提示吗？
谢谢。
编辑：
这是“方形”输出的图片（这是在 Eclipse 中）。