java - 如何获取树的所有叶节点？

Question

假设我在一棵树中有一个节点，如何获取所有祖先为该节点的叶节点？

我已经这样定义了 TreeNode:

public class TreeNode<T>
{
    /** all children of the node */
    private List<TreeNode<T>> children = new ArrayList<TreeNode<T>>();
    /** the parent of the node, if the node is root, parent = null */
    private TreeNode<T> parent = null;
    /** the stored data of the node */
    private T data = null;

    /** the method I want to implement */
    public Set<TreeNode<T>> getAllLeafNodes()
    {
        Set<TreeNode<T>> leafNodes = new HashSet<TreeNode<T>>();
        return leafNodes;
    }
}

Answer 1

使用递归。

• 如果节点本身是一片叶子，则返回它
• 否则，返回其子节点的所有叶节点

像这样(未测试):

public Set<TreeNode<T>> getAllLeafNodes() {
    Set<TreeNode<T>> leafNodes = new HashSet<TreeNode<T>>();
    if (this.children.isEmpty()) {
        leafNodes.add(this);
    } else {
        for (TreeNode<T> child : this.children) {
            leafNodes.addAll(child.getAllLeafNodes());
        }
    }
    return leafNodes;
}