513.找树左下角的值  

class Solution {public int findBottomLeftValue(TreeNode root) {int res = 0;if(root == null){return res;}Queue<TreeNode> que = new LinkedList<>();que.add(root);while(!que.isEmpty()){int size = que.size();for(int i = 0;i < size;i++){TreeNode node = que.poll();//每层遍历将第一个元素赋值if(i == 0) res = node.val;if(node.left != null) que.add(node.left);if(node.right != null) que.add(node.right);}}return res;}
}