原文地址：Print Ancestors of a given node in Binary Tree

已知一个二叉树和一个key，写一个函数打印出这个二叉树中已知节点的所有祖先节点。

例如：如果已知的树是下面的二叉树，而且key是7，然后你的function应该打印出4,2和1。

              1
            /   \           2      3
        /  \       4     5
     /
    7

// Java program to print ancestors of given node

/* A binary tree node has data, pointer to left child
   and a pointer to right child */
class Node 
{
    int data;
    Node left, right, nextRight;

    Node(int item) 
    {
        data = item;
        left = right = nextRight = null;
    }
}

class BinaryTree 
{
    Node root;

    /* If target is present in tree, then prints the ancestors
       and returns true, otherwise returns false. */
    boolean printAncestors(Node node, int target) 
    {
         /* base cases */
        if (node == null)
            return false;

        if (node.data == target)
            return true;

        /* If target is present in either left or right subtree 
           of this node, then print this node */
        if (printAncestors(node.left, target)
                || printAncestors(node.right, target)) 
        {
            System.out.print(node.data + " ");
            return true;
        }

        /* Else return false */
        return false;
    }

    /* Driver program to test above functions */
    public static void main(String args[]) 
    {
        BinaryTree tree = new BinaryTree();

        /* Construct the following binary tree
                  1
                /   \
               2     3
              /  \
             4    5
            /
           7
        */
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.left.left.left = new Node(7);

        tree.printAncestors(tree.root, 7);

    }
}

// This code has been contributed by Mayank Jaiswal

输出：

4 2 1

时间复杂度是：O(n)，在这里n是已知二叉树中节点的数目。