LintCode: Binary Tree Inorder Traversal

C++，递归，辅助函数

 1 /**
 2  * Definition of TreeNode:
 3  * class TreeNode {
 4  * public:
 5  *     int val;
 6  *     TreeNode *left, *right;
 7  *     TreeNode(int val) {
 8  *         this->val = val;
 9  *         this->left = this->right = NULL;
10  *     }
11  * }
12  */
13 class Solution {
14     /**
15      * @param root: The root of binary tree.
16      * @return: Inorder in vector which contains node values.
17      */
18 public:
19     vector<int> inorderTraversal(TreeNode *root) {
20         // write your code here
21         vector<int> result;
22         if (root == NULL) {
23             return result;
24         } else {
25             inorderCore(root, result);
26         }
27         return result;
28     }
29     void inorderCore(TreeNode *root, vector<int> &result) {
30         if (root->left != NULL) {
31             inorderCore(root->left, result);
32         }
33         result.push_back(root->val);
34         if (root->right != NULL) {
35             inorderCore(root->right, result);
36         }
37     }
38 };

C++，递归

 1 /**
 2  * Definition of TreeNode:
 3  * class TreeNode {
 4  * public:
 5  *     int val;
 6  *     TreeNode *left, *right;
 7  *     TreeNode(int val) {
 8  *         this->val = val;
 9  *         this->left = this->right = NULL;
10  *     }
11  * }
12  */
13 class Solution {
14     /**
15      * @param root: The root of binary tree.
16      * @return: Inorder in vector which contains node values.
17      */
18 public:
19     vector<int> inorderTraversal(TreeNode *root) {
20         // write your code here
21         vector<int> result;
22         if (root == NULL) {
23             return result;
24         }
25         if (root->left != NULL) {
26             vector<int> left = inorderTraversal(root->left);
27             result.reserve(result.size() + left.size());
28             result.insert(result.end(), left.begin(), left.end());
29         }
30         result.push_back(root->val);
31         if (root->right != NULL) {
32             vector<int> right = inorderTraversal(root->right);
33             result.reserve(result.size() + right.size());
34             result.insert(result.end(), right.begin(), right.end());
35         }
36         return result;
37     }
38 };

C++，非递归

 1 /**
 2  * Definition of TreeNode:
 3  * class TreeNode {
 4  * public:
 5  *     int val;
 6  *     TreeNode *left, *right;
 7  *     TreeNode(int val) {
 8  *         this->val = val;
 9  *         this->left = this->right = NULL;
10  *     }
11  * }
12  */
13 class Solution {
14     /**
15      * @param root: The root of binary tree.
16      * @return: Inorder in vector which contains node values.
17      */
18 public:
19     vector<int> inorderTraversal(TreeNode *root) {
20         // write your code here
21         vector<int> result;
22         if (root == NULL) {
23             return result;
24         }
25         stack<TreeNode *> sta;
26         TreeNode *cur = root;
27         while (cur != NULL || !sta.empty()) {
28             while(cur != NULL) {
29                 sta.push(cur);
30                 cur = cur->left;
31             }
32             cur = sta.top();
33             sta.pop();
34             result.insert(result.end(), cur->val);
35             cur = cur->right;
36         }
37         return result;
38     }
39 };