leetcode[145]Binary Tree Postorder Traversal
Given a binary tree, return the postorder traversal of its nodes' values.
For example:
Given binary tree {1,#,2,3}
,
1 \ 2 / 3
return [3,2,1]
.
Note: Recursive solution is trivial, could you do it iteratively?
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: vector<int> postorderTraversal(TreeNode *root) { vector<int> res; if(root==NULL)return res; map<TreeNode *, int> smap; smap[root]=0; stack<TreeNode *> sta; sta.push(root); while(!sta.empty()) { TreeNode *p=sta.top(); if((!p->right&&!p->left)||smap.count(p->right)||smap.count(p->left)) { res.push_back(p->val); smap[p]=1; sta.pop(); } else { if(p->right&&!smap.count(p->right)) { sta.push(p->right); smap[p->right]=0; } if(p->left&&!smap.count(p->left)) { sta.push(p->left); smap[p->left]=0; } } } return res; } /** void postorder(vector<int> & res,TreeNode *root) { if(root==NULL)return; postorder(res,root->left); postorder(res,root->right); res.push_back(root->val); } vector<int> postorderTraversal(TreeNode *root) { vector<int> res; postorder(res,root); return res; } */ };