LeetCode-Binary Tree Level Order Traversal

对二叉树进行层序遍历，具体可以参考二叉树相关知识点总结。

/**
 * 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>> result;
        if(root==nullptr) return result;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            int n=q.size();
            vector<int> tRes;
            for(int i=0;i<n;i++){
                TreeNode* t=q.front();
                q.pop();
                tRes.push_back(t->val);
                if(t->left) q.push(t->left);
                if(t->right) q.push(t->right);
            }
            result.push_back(tRes);
        }
        return result;
    }
};