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BinaryTreePostorderTraversal.cpp
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BinaryTreePostorderTraversal.cpp
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/*
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?
*/
class Solution {
public:
vector<int> postorderTraversal(TreeNode *root) {
return postorderTraversal_1(root); // iterative method
return postorderTraversal_2(root); //recursive method
}
vector<int> postorderTraversal_1(TreeNode *root) {
vector<int> res;
stack<TreeNode *> stk;
TreeNode *cur = root;
while (cur||!stk.empty())
{
if(cur)
{
stk.push(cur);
cur = cur->left;
}
else if(!stk.empty())
{
if(stk.top()->right)
cur = stk.top()->right;
else
{
TreeNode *child = stk.top();
res.push_back(child->val);
stk.pop();
while(!stk.empty()&&stk.top()->right==child)
{
res.push_back(stk.top()->val);
child = stk.top();
stk.pop();
}
if(stk.empty())
break;
else if (stk.top()->right!=child)
cur = stk.top()->right;
}
}
}
return res;
}
// second method
vector<int> postorderTraversal_2(TreeNode *root)
{
vector<int> res;
postorderRe(root,res);
return res;
}
void postorderRe(TreeNode *root,vector<int> &res)
{
if(!root)
return;
postorderRe(root->left,res);
postorderRe(root->right,res);
res.push_back(root->val);
}
};