LeetCode Binary Tree Level Order Traversal

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

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

    3
   / \
  9  20
    /  \
   15   7

 

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

 分层遍历二叉树，用队列模拟。

 

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
            List<List<Integer>> soluList=new ArrayList<List<Integer>>();
        if (root==null) {
            return soluList;
        }
        LinkedList<TreeNode> queue=new LinkedList<>();
        queue.push(root);
        List<Integer> currlist;
        int count=1;
        TreeNode node;
        int currlevel=0;
        while (!queue.isEmpty()) {
                currlist=new ArrayList<>();
                currlevel=0;
            for (int i = 0; i < count; i++) {
                node=queue.pop();
                currlist.add(node.val);
                if (node.left!=null) {
                    ++currlevel;
                    queue.add(node.left);
                }
                if (node.right!=null) {
                    ++currlevel;
                    queue.add(node.right);
                }
                
            }
            count=currlevel;
            soluList.add(currlist);
        }
        return soluList;
    }
}