给定一棵二叉树的根节点 root ，请找出该二叉树中每一层的最大值。
示例1：
输入: root = [1,3,2,5,3,null,9]
输出: [1,3,9]
解释:
1
/ \
3 2
/ \ \
5 3 9 示例2：
输入: root = [1,2,3]
输出: [1,3]
解释:
1
/ \
2 3示例3：
输入: root = [1]
输出: [1]示例4：
输入: root = [1,null,2]
输出: [1,2]
解释:
1
\
2 示例5：
输入: root = []
输出: []提示：
- 二叉树的节点个数的范围是
[0,104] -231 <= Node.val <= 231 - 1
//leetcode submit region begin(Prohibit modification and deletion)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public int findBottomLeftValue(TreeNode root) {
int result = -1;
Queue<TreeNode> nodeQ = new LinkedList<>();
if (root == null) {
return result;
}
int nodeNum = 1;
nodeQ.add(root);
while (!nodeQ.isEmpty()) {
for (int i = 0; i < nodeNum; i++) {
TreeNode node = nodeQ.poll();
if (i == 0) {
result = node.val;
}
if (node.left != null) {
nodeQ.add(node.left);
}
if (node.right != null) {
nodeQ.add(node.right);
}
}
nodeNum = nodeQ.size();
}
return result;
}
}
//leetcode submit region end(Prohibit modification and deletion)
