Binary Tree Level Order Traversal

/**
 * 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)
            return result;
        int now=1;
        int next=0;
        queue<TreeNode*> q;
        q.push(root);
        vector<int> level;
        while(now)
        {
            level.push_back(q.front()->val);
            now--;
            if(q.front()->left)
            {
                q.push(q.front()->left);
                next++;
            }
            if(q.front()->right)
            {
                q.push(q.front()->right);
                next++;
            }
            q.pop();
            if(!now)
            {
                result.push_back(level);
                now=next;
                next=0;
                level.clear();
            }
        }
        return result;
    }
};

level.clear():删除vector level中的所有元素，返回void。