482. Binary Tree Level Sum
Given a binary tree and an integer which is the depth of the target level.
Calculate the sum of the nodes in the target level.
Example
Example 1:
Input:
1
/
2 3
/ /
4 5 6 7
/
8 9
and depth=2
Output:5
Example 2:
Input:
1
/
2 3
/ /
4 5 6 7
/
8 9
and depth=3
Output:22
思路:递归法