LeetCode: Find Largest Value in Each Tree Row

BFS

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public List<Integer> largestValues(TreeNode root) {
         List<Integer> ans = new ArrayList<Integer>();
         if (root == null) return ans;
         Queue<TreeNode> queue = new LinkedList<TreeNode>();
         queue.add(root);
         while (queue.isEmpty() != true) {
             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.add(node.left);
                 if (node.right != null) queue.add(node.right);
             }
             ans.add(max);
         }
         return ans;
     }
 }