Binary Tree Level Order Traversal
给一个二叉树, 层序扫描. 这个最常见的扫描方法.
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/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public List<List<Integer>> levelOrder(TreeNode root) { ArrayList<List<Integer>> res = new ArrayList<List<Integer>>(); if(root == null) return res; Queue<TreeNode> queue = new LinkedList<TreeNode>(); queue.offer(root); while(!queue.isEmpty()){ List<Integer> tmp = new ArrayList<Integer>(); int size = queue.size(); for(int i = 0 ; i < size; i++) { TreeNode node = queue.poll(); tmp.add(node.val); if(node.left != null) queue.offer(node.left); if(node.right != null) queue.offer(node.right); } res.add(tmp); } return res; } } |