offer2-45

给定一个二叉树的 根节点 root，请找出该二叉树的 最底层 最左边 节点的值。

假设二叉树中至少有一个节点。

示例 1:

输入: root = [2,1,3]
输出: 1

示例 2:

输入: [1,2,3,4,null,5,6,null,null,7]
输出: 7

提示:

• 二叉树的节点个数的范围是 [1,104]
• -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)