原文地址：Print nodes at k distance from root
已知一个树的根节点，一个整数k。打印出所有距离根节点为k的节点。
例如，在下面的树中， 4, 5 & 8距离根节点的距离是2。
这个问题可以用递归来解决。
// Java program to print nodes at k distance from root /* A binary tree node has data, pointer to left child and a pointer to right child */ class Node { int data; Node left, right; Node(int item) { data = item; left = right = null; } } class BinaryTree { Node root; void printKDistant(Node node, int k) { if (node == null) return; if (k == 0) { System.out.print(node.data + " "); return; } else { printKDistant(node.left, k - 1); printKDistant(node.right, k - 1); } } /* Driver program to test above functions */ public static void main(String args[]) { BinaryTree tree = new BinaryTree(); /* Constructed binary tree is 1 / \ 2 3 / \ / 4 5 8 */ 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.right.left = new Node(8); tree.printKDistant(tree.root, 2); } } // This code has been contributed by Mayank Jaiswal上面的代码输出4,5和8。
时间复杂度是：O(n)，在这里n是已知二叉树中节点的数目。
