1 /** 2 * Definition for binary tree 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */ 10 class Solution { 11 public: 12 vector<int> postorderTraversal(TreeNode *root) { 13 vector<int> res; 14 if(root == NULL) 15 return res; 16 stack<TreeNode*> node; 17 node.push(root); 18 TreeNode* pre, *cur; 19 pre = root; 20 while(!node.empty()) 21 { 22 cur = node.top(); 23 if(cur->left == pre || cur->right == pre || (cur->left == NULL && cur->right == NULL)) 24 { 25 res.push_back(cur->val); 26 node.pop(); 27 pre = cur; 28 } 29 else 30 { 31 if(cur->right != NULL) 32 node.push(cur->right); 33 34 if(cur->left != NULL) 35 node.push(cur->left); 36 } 37 } 38 return res; 39 } 40 };