Binary Tree Level Order Traversal

最新推荐文章于 2025-12-11 15:34:25 发布

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本文介绍了一种解决二叉树层次遍历问题的方法。通过递归的方式记录每一层节点的值，最终得到从上到下、从左到右的层次遍历结果。

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.

其实随便怎么traverse,只需要知道你的level就行了。。。。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int> > levelOrder(TreeNode *root) {
        vector< vector<int> > res;
        helper(root,res,0);
        return res;
    }
    
    void helper(TreeNode* root, vector<vector<int> >& res, int level){
        if (root==0)
            return;
        if (res.size()==level)
            res.push_back(vector<int>());
        res[level].push_back(root->val);
        
        helper(root->left,res, level+1);
        helper(root->right,res,level+1);
    }
};