Binary Tree Level Order Traversal

最新推荐文章于 2025-12-28 16:25:57 发布

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本文详细介绍了如何实现二叉树的层次遍历，包括使用队列进行层次遍历的算法步骤和代码实现。

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},

return its level order traversal as:

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

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

/**
 * 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) {
        LinkedList<TreeNode> stack=new LinkedList<TreeNode>();
        LinkedList<TreeNode> curr=new LinkedList<TreeNode>();
        List<List<Integer>> res=new ArrayList< List<Integer> >();
        if(root==null) return res;
        stack.add(root);
        
        while(!stack.isEmpty()){
            curr=stack;
            stack=new LinkedList<TreeNode>();
            List<Integer> a=new LinkedList<Integer>();
            while(curr.size()>0){
                TreeNode tmpNode=curr.peekFirst();
                if(tmpNode.left!=null) stack.add(tmpNode.left);
                if(tmpNode.right!=null) stack.add(tmpNode.right);
                a.add(tmpNode.val);
                curr.poll();
            }
            res.add(a);
        }
        return res;
    }
}