Node at distance
Medium Accuracy: 45.37% Submissions: 11492 Points: 4

Given a Binary Tree and a positive integer k. The task is to count all distinct nodes that are distance k from a leaf node. A node is at k distance from a leaf if it is present k levels above the leaf and also, is a direct ancestor of this leaf node. If k is more than the height of Binary Tree, then nothing should be counted.

Example 1:

Input:
        1
      /   \
     2     3
   /  \   /  \
  4   5  6    7
          \ 
          8
K = 2
Output: 2
Explanation: There are only two unique
nodes that are at a distance of 2 units
from the leaf node. (node 3 for leaf
with value 8 and node 1 for leaves with
values 4, 5 and 7)
Note that node 2
isn't considered for leaf with value
8 because it isn't a direct ancestor
of node 8.

Example 2:

Input:
          1
         /
        3
       /
      5
    /  \
   7    8
         \
          9
K = 4
Output: 1
Explanation: Only one node is there
which is at a distance of 4 units
from the leaf node.(node 1 for leaf
with value 9) 

Your Task:
You don't have to read input or print anything. Complete the function printKDistantfromLeaf() that takes root node and k as inputs and returns the number of nodes that are at distance k from a leaf node. Any such node should be counted only once. For example, if a node is at a distance k from 2 or more leaf nodes, then it would add only 1 to our count.

Expected Time Complexity: O(N).
Expected Auxiliary Space: O(Height of the Tree).

Constraints:
1 <= N <= 105

Note: The Input/Output format and Example are given are used for the system's internal purpose, and should be used by a user for Expected Output only. As it is a function problem, hence a user should not read any input from the stdin/console. The task is to complete the function specified, and not to write the full code.

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