标签：efi lex input its uri traversal output can c++
Preorder:
Given a binary tree, return the preorder traversal of its nodes‘ values.
Example:
Input:[1,null,2,3]1 2 / 3 Output:[1,2,3]
Approach #1: Recurisive.
/**
* 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> ans;
helper(root, ans);
return ans;
}
private:
void helper(TreeNode* root, vector<int>& ans) {
if (root == NULL) return ;
ans.push_back(root->val);
helper(root->left, ans);
helper(root->right, ans);
}
};
Approach #2: Iteratively.[Java]
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<Integer> preorderTraversal(TreeNode root) {
List<Integer> res = new LinkedList<Integer>();
Stack<TreeNode> todo = new Stack<TreeNode>();
TreeNode cur = root;
while (cur != null) {
res.add(cur.val);
if (cur.right != null) {
todo.push(cur.right);
}
cur = cur.left;
if (cur == null && !todo.isEmpty()) {
cur = todo.pop();
}
}
return res;
}
}
Approach #3: Morris Traversal.[C++]
/**
* 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) {
TreeNode* cur = root;
vector<int> nodes;
while (cur) {
if (cur->left) {
TreeNode* pre = cur->left;
while (pre->right && (pre->right != cur)) {
pre = pre->right;
}
if (!(pre->right)) {
nodes.push_back(cur->val);
pre->right = cur;
cur = cur->left;
} else {
pre->right = NULL;
cur = cur->right;
}
} else {
nodes.push_back(cur->val);
cur = cur->right;
}
}
return nodes;
}
};
Using Morris Traversal can don‘t use recurisive and stack and space complex is O(1).
标签：efi lex input its uri traversal output can c++
原文地址：https://www.cnblogs.com/ruruozhenhao/p/9978743.html
