Binary Tree inorder/preorder traversal

Given a binary tree, the system returns all elements traversed in ascending or descending order of a set.

There are two methods: one is the classic Recursive Method of the classic middle-order/first-order method, and the other can be combined with the stack to implement non-recursive

 

Given a binary tree, returnInorderTraversal of its nodes 'values.

For example:
Given Binary Tree{1,#,2,3},

   1         2    /   3

 

Return[1,3,2].

OJ's binary tree serialization:

The serialization of a binary tree follows a level order traversal, where '# 'signiies a path Terminator where no node exists below.

Here's an example:

   1  /  2   3    /   4         5

The above binary tree is serialized "{1,2,3,#,#,4,#,#,5}".

 1 /** 2  * Definition for binary tree 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     vector<int> inorderTraversal(TreeNode *root) {13         vector<int> ret;14         if(root == NULL)15             return ret;16             17         stack<TreeNode *> stack;18         stack.push(root);19         20         while(!stack.empty()){21             TreeNode *node = stack.top();22             stack.pop();23             if(node->left == NULL && node->right == NULL){24                 ret.push_back(node->val);25             }26             else{27                 if(node->right != NULL)28                     stack.push(node->right);29                 stack.push(node);30                 if(node->left != NULL)31                     stack.push(node->left);32                     33                 node->left = node->right = NULL;34             }35             36         }37         38         return ret;39             40     }41 };

 

Given a binary tree, returnPreorderTraversal of its nodes 'values.

For example:
Given Binary Tree{1,#,2,3},

   1         2    /   3

 

Return[1,2,3].

As required above, only elements in a sequence in the middle order are returned. This time, Recursive Implementation is used:

 1 /** 2  * Definition for binary tree 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     vector<int> preorderTraversal(TreeNode *root) {13         vector<int> ret;14         if(root == NULL)15             return ret;16         PreorderTraversal(root,ret);17         return ret;18     }19     20     void PreorderTraversal(TreeNode *root,vector<int> &ret){21         if(root != NULL){22             ret.push_back(root->val);23             PreorderTraversal(root->left,ret);24             PreorderTraversal(root->right,ret);25         }26     }27 };

 

Binary Tree inorder/preorder traversal