My BFS solution:
/** * 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 List<Integer> largestValues(TreeNode root) { List<Integer> res = new ArrayList<>(); if(root==null) return res; Queue<TreeNode> queue = new LinkedList<>(); queue.offer(root); while(!queue.isEmpty()){ int size = queue.size(); int max = Integer.MIN_VALUE; for(int i=0;i<size;i++){ TreeNode node = queue.poll(); max = Math.max(max, node.val); if(node.left!=null) queue.offer(node.left); if(node.right!=null) queue.offer(node.right); } res.add(max); } return res; } }