leetCode . Binary Tree Inorder/ Preorder/ Post Traversal iteratively
2016-06-14 11:23
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问题
https://leetcode.com/problems/binary-tree-inorder-traversal/https://leetcode.com/problems/binary-tree-postorder-traversal/
https://leetcode.com/problems/binary-tree-preorder-traversal/
解法
http://www.cnblogs.com/AnnieKim/archive/2013/06/15/morristraversal.htmlInorder 时间复杂度 3N 空间复杂度 O（1）
/**
* 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> inorderTraversal(TreeNode* root) {
vector<int> ret;
TreeNode* cur = root;
while(cur != NULL)
{
if (cur->left == NULL)
{
ret.push_back(cur->val);
cur = cur->right;
}
else
{
TreeNode * pre = cur->left;
while(pre->right != NULL && pre->right != cur)
pre = pre->right;
if (pre->right == NULL)
{
pre->right = cur;
cur = cur->left;
}
else
{
pre->right = NULL;
ret.push_back(cur->val);
cur = cur->right;
}
}
}
return ret;
}
};Preorder 时间复杂度 3N 空间复杂度 O（1）
/**
* 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> preorderTraversal(TreeNode* root) {
vector<int> ret;
TreeNode *cur = root;
while(cur != NULL)
{
if (cur->left == NULL)
{
ret.push_back(cur->val);
cur = cur->right;
}
else
{
TreeNode * pre = cur->left;
while(pre->right != NULL && pre->right != cur)
pre = pre->right;
if (pre->right == NULL)
{
ret.push_back(cur->val);
pre->right = cur;
cur = cur->left;
}else
{
pre->right = NULL;
cur = cur->right;
}
}
}
return ret;
}
};
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