class Solution {public:	vector
     
       postorderTraversal(TreeNode* root) {		vector
      
        vec;		travel(root, vec);		return vec;	}       //后序遍历	void travel(TreeNode* root, vector
       
        & v)	{		if (root == NULL)return;		travel(root->left,v);		travel(root->right, v);		v.push_back(root->val); 	}       //前序遍历	void pretravel(TreeNode* root, vector
        
         & v)	{		if (root == NULL)return;		travel(root->left,v);		travel(root->right, v);		v.push_back(root->val); 	}               //中序遍历	void midtravel(TreeNode* root, vector
         
          & v)	{		if (root == NULL)return;		travel(root->left,v);		v.push_back(root->val); 		travel(root->right, v);	}     };