题目链接

层序遍历

思路：使用层序遍历，记录每一行 i = 0 的元素，就可以找到树左下角的值

/*** 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) {Deque<TreeNode> queue = new LinkedList<TreeNode>();int res = root.val;queue.offer(root);while(!queue.isEmpty()){int size = queue.size();for(int i = 0; i < size; i++){TreeNode node = queue.poll();if(i == 0){res = node.val;}if(node.left != null){queue.offer(node.left);}if(node.right != null){queue.offer(node.right);}}}return res;}
}