Find Largest Value in Each Tree Row

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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]

思路：BFS，用queue来收集每行的node，取最大值即可；

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Integer> largestValues(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        if(root == null) return list;
        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
        queue.add(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            int curMax = Integer.MIN_VALUE;
            while(size>0){
                TreeNode node = queue.poll();
                size--;
                curMax = Math.max(curMax,node.val);
                if(node.left!=null){
                    queue.add(node.left);
                }
                if(node.right!=null){
                    queue.add(node.right);
                }
            }
            list.add(curMax);
        }
        return list;
    }
}