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145bstpostorder.cpp
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145bstpostorder.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?
/**
* Definition for a binary tree node.
* 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>result;
if ( NULL == root)
{
return result;
}
stack<TreeNode*>s;
s.push(root);
TreeNode* prev = NULL, *cur = NULL;
while(!s.empty())
{
cur = s.top();
if ( !prev || prev->left == cur || prev->right == cur)
{
if (cur->left)
{
s.push(cur->left);
}
else if ( cur->right)
{
s.push(cur->right);
}
else
{
s.pop();
result.push_back(cur->val);
}
}
else if (cur->left == prev)
{
if ( cur->right)
{
s.push(cur->right);
}
else
{
s.pop();
result.push_back(cur->val);
}
}
else if (cur->right == prev)
{
s.pop();
result.push_back(cur->val);
}
prev = cur;
}
}
};