Binary Tree Level Order Traversal

最新推荐文章于 2022-02-20 23:20:19 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，并提供了一个C++实现示例。该算法采用递归方式，从根节点开始，按层级顺序返回各节点的值。

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]
]

/**
 * 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> > res;
	void traversal( int level, TreeNode* root)
	{
		if (0 == root) return;
		if (level + 1 > res.size())
		{
			vector<int> vec;
			vec.push_back(root->val);
			res.push_back(vec);
		}
		else
		{
			res[level].push_back(root->val);
		}
		traversal(level + 1, root->left);
		traversal(level + 1, root->right);
	}
    vector<vector<int> > levelOrder(TreeNode *root)
	{
        res.clear();
		traversal(0, root);
		return res;
    }
};