102. Binary Tree Level Order Traversal

Posted 2020-07-06 我的名字叫周周

    /*
     * 102. Binary Tree Level Order Traversal 
     * 11.21 by Mingyang 最基本的queue的做法
     */
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> results = new ArrayList<List<Integer>>();
        ArrayList<Integer> result = new ArrayList<Integer>();
        if (root == null)
            return results;
        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
        queue.add(root);
        int currentNumber = 1;
        int nextNumber = 0;
        while (queue.size() != 0) {
            TreeNode temp = queue.poll();
            result.add(temp.val);
            currentNumber--;
            if (temp.left != null) {
                queue.add(temp.left);
                nextNumber++;
            }
            if (temp.right != null) {
                queue.add(temp.right);
                nextNumber++;
            }
            if (currentNumber == 0) {
                results.add(result);
                currentNumber = nextNumber;
                nextNumber = 0;
                result = new ArrayList<Integer>();
            }
        }
        return results;
    }