[leetcode] Binary Tree Level Order Traversal

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本文详细介绍了如何解决LeetCode上的二叉树层次遍历问题，通过使用队列实现从左到右、逐层遍历节点值，并提供了具体的代码实现和示例解析。

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

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 a binary tree node.
 * 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>> vct;
        if(!root) return vct;
		vector<TreeNode> box;
        box.push_back(*root);
        int num1 = 1, num2=0;
        while(num1) {
            vector<int> curVct;
			while(num1) {
				TreeNode node = box.front();
				curVct.push_back(node.val);
				box.erase(box.begin());
				num1--;
				if(node.left) {box.push_back(*node.left); num2++;}
				if(node.right){box.push_back(*node.right);num2++;}
            }
			vct.push_back(curVct);
			num1=num2;
			num2=0;
        }
		return vct;
    }
};