Java for LeetCode 107 Binary Tree Level Order Traversal II

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree {3,9,20,#,#,15,7},

return its bottom-up level order traversal as:

[

  [15,7],

  [9,20],

  [3]

]

解题思路：

修改下Java for LeetCode 102 Binary Tree Level Order Traversal即可解决，JAVA实现如下：

    public List<List<Integer>> levelOrderBottom(TreeNode root) {

	    List<List<Integer>> list = new ArrayList<List<Integer>>();

	    if (root == null)

	        return list;

	    Queue<TreeNode> queue = new LinkedList<TreeNode>();

	    queue.add(root);

	    while (queue.size() != 0) {

	        List<Integer> alist = new ArrayList<Integer>();

	        for (TreeNode child : queue)

	            alist.add(child.val);

	        list.add(new ArrayList<Integer>(alist));

	        Queue<TreeNode> queue2=queue;

	        queue=new LinkedList<TreeNode>();

	        for(TreeNode child:queue2){

	            if (child.left != null)

	                queue.add(child.left);

	            if (child.right != null)

	                queue.add(child.right);

	        }

	    }

	    Collections.reverse(list);

	    return list;

    }

巴特西

Java for LeetCode 107 Binary Tree Level Order Traversal II

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