数据结构——查找二叉树已知节点的祖先节点

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。