【算法11】-【二叉树的层序遍历】
广度优先搜索算法
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public List<List<Integer>> levelOrder(TreeNode root) { List<List<Integer>> ret = new ArrayList<List<Integer>>(); if (root == null) { return ret; } Queue<TreeNode> queue = new LinkedList<TreeNode>(); queue.offer(root); while (!queue.isEmpty()) { List<Integer> level = new ArrayList<Integer>(); int currentLevelSize = queue.size(); for (int i = 1; i <= currentLevelSize; ++i) { TreeNode node = queue.poll(); level.add(node.val); if (node.left != null) { queue.offer(node.left); } if (node.right != null) { queue.offer(node.right); } } ret.add(level); } return ret; } }