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
注意：
- sum 定义为类成员变量
代码：
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/ public class Solution {
/**
* @param root: the root of the binary tree
* @param level: the depth of the target level
* @return: An integer
*/
int sum = 0;
public int levelSum(TreeNode root, int level) {
helper(root, 1, level);
return sum;
}
public void helper(TreeNode root, int depth, int level) {
if (root == null) {
return;
} if (depth == level) {
sum += root.val;
return;
} helper(root.left, depth + 1, level);
helper(root.right, depth + 1, level);
}
}