【LeetCode】102. 二叉树的层次遍历

LeetCode:https://leetcode-cn.com/problems/binary-tree-level-order-traversal/

给定一个二叉树，返回其按层次遍历的节点值。 （即逐层地，从左到右访问所有节点）。

例如:
给定二叉树: [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

返回其层次遍历结果：

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

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int TreeHeight(TreeNode* root)
    {
        if(!root)
            return 0;
        int lefth  = TreeHeight(root->left);
        int righth = TreeHeight(root->right);
        return lefth > righth ? lefth + 1 : righth + 1;
    }
    vector<vector<int>> levelOrder(TreeNode* root) {
        queue<TreeNode*> nodeq;
        queue<int> levelq;
        vector<vector<int>> v;
        if(root)
        {
            nodeq.push(root);
            levelq.push(1);
        }
        v.resize(TreeHeight(root));
        while(!nodeq.empty())
        {
            TreeNode* node = nodeq.front();
            nodeq.pop();
            int level = levelq.front();
            levelq.pop();
            v[level - 1].push_back(node->val);
            
            if(node->left)
            {
                nodeq.push(node->left);
                levelq.push(level+1);
            }
            if(node->right)
            {
                nodeq.push(node->right);
                levelq.push(level+1);
            }
        }
        return v;
    }
};