代码随想录：513. 找树左下角的值

513. 找树左下角的值

使用层序遍历，找到最后一层时输出即可

/**
 * 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> q=new LinkedList<>();
        q.add(root);
        TreeNode last=root;
        int sum=0;
        TreeNode head=root;
        while(!q.isEmpty())
        {
            TreeNode cur=q.poll();
            if(cur.left!=null){q.add(cur.left);sum++;}
            if(cur.right!=null){q.add(cur.right);sum++;}
            if(cur==last)
            {
              if(sum==0)
              {
                return head.val;
              }
              sum=0;
              head=q.peekFirst();
             last=q.peekLast();
            }
        }
        return 0;
    }
}