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},

    3
   /   9  20
    /     15   7

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

class Solution {
public:
    vector<vector<int> > levelOrder(TreeNode *root) {
        vector< vector<int> > qh;
        vector<int> arr(0);
        queue<TreeNode*> q;
        int cnt=1,i;
        int leaves=0;
        
        TreeNode *p = root;
        if(p==NULL) return qh;
        q.push(p);
        while(!q.empty()){
            arr.clear();
            for(i=0,leaves=0;i<cnt;i++){
                p=q.front();
                arr.push_back(p->val);
                q.pop();
                if(p->left!=NULL) {
                    q.push(p->left);
                    leaves++;
                }
                if(p->right!=NULL) {
                    q.push(p->right);
                    leaves++;
                }
            }
            cnt=leaves;
            qh.push_back(arr);
            
        }
        return qh;
    }
};

Binary Tree Level Order Traversal