Find Bottom Left Tree Value

题目地址：
https://leetcode.com/problems/find-bottom-left-tree-value/description/

题目：

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:

Input:

    2
   / \
  1   3

Output:
1

Example 2: 

Input:

        1
       / \
      2   3
     /   / \
    4   5   6
       /
      7

Output:
7

Note: You may assume the tree (i.e., the given root node) is not NULL.

解题思路：
bfs

代码：

    public int findLeftMostNode(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            root = queue.poll();
            if (root.right != null)
                queue.add(root.right);
            if (root.left != null)
                queue.add(root.left);
        }
        return root.val;
    }