leetcode 102 Binary Tree Level Order Traversal ----- java
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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,null,null,15,7]
,
3 / 9 20 / 15 7
return its level order traversal as:
[ [3], [9,20], [15,7] ]
输出一棵树的每一行,很简单。
/** * 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) { List list = new ArrayList<List<Integer>>(); if( root == null) return list; Queue<TreeNode> queue = new LinkedList<TreeNode>(); queue.add(root); while( !queue.isEmpty() ){ List ans = new ArrayList<Integer>(); int size = queue.size(); for( int i = 0;i<size;i++){ TreeNode node = queue.poll(); if( node == null) continue; ans.add(node.val); queue.add(node.left); queue.add(node.right); } if( ans.size() != 0) list.add(ans); } return list; } }
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