0515.在每個樹行中找最大值

描述

您需要在二叉樹的每一行中找到最大的值。

例項

輸入: 

          1
         / \
        3   2
       / \   \  
      5   3   9 

輸出: [1, 3, 9]

題解

逐層遍歷,對每一層找到最大值

	public ArrayList<TreeNode> getNextLayNodes(ArrayList<TreeNode> layList1){
        ArrayList<TreeNode> layList2 =
 
 new ArrayList<>();
        for(TreeNode node:layList1){
            if (node.left != null)
                layList2.add(node.left);
            if (node.right != null)
                layList2.add(node.right);
        }
        return layList2;
    }

    public List<Integer> largestValues
 
(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        if (root == null)
            return result;
        ArrayList<TreeNode> layList1;
        ArrayList<TreeNode> layList2;
        layList1 = new ArrayList<>();
        layList1.add(root);
        
        while
 
 (!layList1.isEmpty()){
            layList2 = getNextLayNodes(layList1);
            int max = Integer.MIN_VALUE;
            for (TreeNode node:layList1)
                max = max > node.val ? max : node.val;
            result.add(max);
            layList1 = layList2;
        }
        
        return result;
    }