515.Find Largest Value in Each Tree Row

You need to find the largest value in each row of a binary tree.
Example:?
Input: 

          1
         /         3   2
       /      
      5   3   9 

Output: [1,3,9]
Bfs
 public int[] findValueMostElement(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        List<Integer> res = new ArrayList<Integer>();
        queue.add(root);
        int queueSize = root == null ? 0 : 1;
        while (queueSize > 0) {
            int largestElement = Integer.MIN_VALUE;
            for (int i=0;i<queueSize;i++) {
                TreeNode cur = queue.poll();
                largestElement = Math.max(cur.val,largestElement);
                if (cur.left != null) queue.add(cur.left);
                if (cur.right != null) queue.add(cur.right);
            }
            res.add(largestElement);
            queueSize = queue.size();
        }
        int[] resArray = new int[res.size()];
        for (int i=0;i<res.size();i++) resArray[i] = res.get(i);
        return resArray;
    }




Dfs
Just a simple pre-order traverse idea. Use depth to expand result list size and put the max value in the appropriate position.

public class Solution {
    public List<Integer> largestValues(TreeNode root) {
        List<Integer> res = new ArrayList<Integer>();
        helper(root,res,0);
        return res;
    }
    private void helper(TreeNode root,List<Integer> res,int d){
        if(root == null){
            return;
        }
       //expand list size
        if(d == res.size()){
            res.add(root.val);
        }
        else{
        //or set value
            res.set(d,Math.max(res.get(d),root.val));
        }
        helper(root.left,d+1);
        helper(root.right,d+1);
    }
}