【LeetCode-121】二叉树的层序遍历

struct TreeNode{
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(): val(0),left(nullptr), right(nullptr) {}
    TreeNode(int x): val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode* left, TreeNode* right): val(x), left(left), right(right) {}
};

/*
层序遍历：创建一个辅助队列，利用队列先进先出的特点，使用广度优先遍历实现层序遍历
*/
class Solution{
public:
    vector<vector<int>> levelOrder(TreeNode* root)
    {
        queue<TreeNode*> que;
        if(root != nullptr) que.push(root);
        vector<vector<int>> result;
        while(!que.empty())
        {
            int size = que.size();
            vetor<int> vec;
            for(int i = 0; i < size; i++)
            {
                TreeNode* node = que.front();
                que.pop();
                vec.push_back(node->val);
                
                if(node->left) que.push(node->left);
                if(node->right) que.push(node->right);
            }
            result.push_back(vec);
        }
        return result;
    }
};