Leetcode 102.二叉树的层序遍历

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> result;
        if(!root) return result;

        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            int levelsize = q.size();
            result.push_back(vector<int>());
            while(levelsize--){
                TreeNode *p = q.front();
                q.pop();
                result.back().push_back(p->val);
                if(p->left) q.push(p->left);
                if(p->right) q.push(p->right);
            }
        }
        return result;
    }
};