LeetCode——Binary Tree Level Order Traversal

標籤：leetcode

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]]

原題連結：https://oj.leetcode.com/problems/binary-tree-level-order-traversal/

題目：給定一個二叉樹，返回節點的層序遍曆的值。（如，從左至右，一層一層）

思路：類似於廣度優先遍曆，可以將節點依次放入到隊列中，再按層取出。

public List<List<Integer>> levelOrder(TreeNode root) {List<List<Integer>> list = new ArrayList<List<Integer>>();if (root == null)return list;Queue<TreeNode> queue = new LinkedList<TreeNode>();queue.add(root);while (!queue.isEmpty()) {List<Integer> li = new ArrayList<Integer>();int size = queue.size();for (int i = 0; i < size; i++) {TreeNode node = queue.poll();li.add(node.val);if (node.left != null)queue.add(node.left);if (node.right != null)queue.add(node.right);}list.add(li);}return list;}// Definition for binary treepublic class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int x) {val = x;}}