原题链接在这里：

题目：

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

Example 1:

Input:    2   / \  1   3Output:1

Example 2: 

Input:        1       / \      2   3     /   / \    4   5   6       /      7Output:7

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

题解：

做从右到左的BFS.

Time Complexity: O(n). n是node个数.

Space: O(n).

AC Java:

1 /** 2  * Definition for a binary tree node. 3  * public class TreeNode { 4  *     int val; 5  *     TreeNode left; 6  *     TreeNode right; 7  *     TreeNode(int x) { val = x; } 8  * } 9  */10 class Solution {11     public int findBottomLeftValue(TreeNode root) {12         LinkedList
     
       que = new LinkedList
      
       ();13         que.add(root);14         while(!que.isEmpty()){15             root = que.poll();16             if(root.right != null){17                 que.add(root.right);18             }19             if(root.left != null){20                 que.add(root.left);21             }22         }23         return root.val;24     }25 }