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struct TreeNode {    int val;    struct TreeNode *left;    struct TreeNode *right;    TreeNode(int x) :    val(x), left(NULL), right(NULL) {    }};class TreeToSequence {    vector
   
     preOrder(TreeNode * root){        vector
    
     ans;        stack
     
       s;        TreeNode * cur = root;        if(cur)            s.push(cur);        while (!s.empty()) {            cur = s.top();            s.pop();            ans.push_back(cur->val);            if(cur->right)                s.push(cur->right);            if(cur->left)                s.push(cur->left);        }        return ans;    }    vector
      
        Inorder(TreeNode * root){        TreeNode * cur = root;        vector
       
        ans;        stack
        
         s; if(cur){ s.push(cur); cur = cur->left; } while (!s.empty()||cur) { if(cur){ s.push(cur); cur = cur->left; } else { TreeNode * node = s.top(); s.pop(); ans.push_back(node->val); cur = node ->right; } } return ans; } vector
         
           postOrder(TreeNode *root){//可以用一个辅助栈实现,但是稍微复杂 这里未写出 stack
          
            inputStack,outputStack; vector
           
            ans; TreeNode * cur = root; if(cur) inputStack.push(cur); while (!inputStack.empty()) { cur = inputStack.top(); inputStack.pop(); outputStack.push(cur); if(cur->left) inputStack.push(cur->left); if(cur->right) inputStack.push(cur->right); } while (!outputStack.empty()) { cur = outputStack.top(); outputStack.pop(); ans.push_back(cur->val); } return ans; }public: vector
            
             
               > convert(TreeNode* root) { vector
              
               
                > ans; ans.push_back(preOrder(root)); ans.push_back(Inorder(root)); ans.push_back(postOrder(root)); return ans; }};
               
              
             
            
           
          
         
        
       
      
     
    
   

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