LINTCODE69 :二叉树的层次遍历

    /*
    @Copyright:LintCode
    @Author:   cindyyao
    @Problem:  http://www.lintcode.com/problem/binary-tree-level-order-traversal
    @Language: Java
    @Datetime: 17-03-14 04:49
    */
     
    /**
     * Definition of TreeNode:
     * public class TreeNode {
     *     public int val;
     *     public TreeNode left, right;
     *     public TreeNode(int val) {
     *         this.val = val;
     *         this.left = this.right = null;
     *     }
     * }
     */
     
     
    public class Solution {
        /**
         * @param root: The root of binary tree.
         * @return: Level order a list of lists of integer
         */
        public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
            // write your code here
            ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
            if (root == null) {
                return result;
            }
            Queue<TreeNode> queue = new LinkedList<>();
            queue.offer(root);
            while (!queue.isEmpty()) {
                int size = queue.size();
                ArrayList<Integer> level = new ArrayList<Integer>();
                for (int i = 0; i < size; i++) {
                    TreeNode currNode = queue.poll();
                    level.add(currNode.val);
                    if (currNode.left != null) {
                        queue.offer(currNode.left);
                    }
                    if (currNode.right != null) {
                        queue.offer(currNode.right);
                    }
                }
                result.add(level);
            }
            return result;
        }
    }