从树中返回值的字符串

Question

好的，所以我想用中序、前序和后序遍历一棵树。我得到了遍历树的正确算法，但我需要 return 形式为 "Node1 Node2 Node3" 的字符串，但我有 "Node1Node2Node3"。这是我的预购代码：

public String PreOrder() {
        /* TODO: Implement */
        StringBuilder string = new StringBuilder();
        preorderRecursive(string, root);
        return string.toString();
    }
    public StringBuilder preorderRecursive(StringBuilder string, Node current){
        if (current != null) {
        string.append(current.key);
        preorderRecursive(string, current.left);
        preorderRecursive(string, current.right);
        }
        return string;
    }

我收到错误 org.junit.ComparisonFailure: expected:<3[ 1 2 8 4 5 7 9 ]10> but was:<3[1284579]10>

Answer 1

只需在 stringBuilder 中添加一个 space，

if (current != null) {
   string.append(current.key).append(" ");
   ...

从树中返回值的字符串

Returning a String of values from a tree

java

string

data-structures

tree

preorder