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 14 class Solution { 15 public: 16 /** 17 * @param root: The root of binary tree. 18 * @return: Preorder in vector which contains node values. 19 */ 20 vector<int> preorderTraversal(TreeNode *root) { 21 // write your code here 22 vector<int> result; 23 if (root == NULL) { 24 return result; 25 } 26 result.insert(result.end(), root->val); 27 if (root->left != NULL) { 28 vector<int> left = preorderTraversal(root->left); 29 result.reserve(result.size()+left.size()); 30 result.insert(result.end(), left.begin(), left.end()); 31 } 32 if (root->right != NULL) { 33 vector<int> right = preorderTraversal(root->right); 34 result.reserve(result.size()+right.size()); 35 result.insert(result.end(), right.begin(), right.end()); 36 } 37 return result; 38 } 39 };
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 14 class Solution { 15 public: 16 /** 17 * @param root: The root of binary tree. 18 * @return: Preorder in vector which contains node values. 19 */ 20 vector<int> preorderTraversal(TreeNode *root) { 21 // write your code here 22 vector<int> result; 23 if (root == NULL) { 24 return result; 25 } else { 26 preorderCore(root, result); 27 } 28 return result; 29 } 30 void preorderCore(TreeNode *root, vector<int> &result) { 31 if (root == NULL) { 32 return ; 33 } 34 result.insert(result.end(), root->val); 35 if (root->left != NULL) { 36 preorderCore(root->left, result); 37 } 38 if (root->right != NULL) { 39 preorderCore(root->right, result); 40 } 41 } 42 };
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 14 class Solution { 15 public: 16 /** 17 * @param root: The root of binary tree. 18 * @return: Preorder in vector which contains node values. 19 */ 20 vector<int> preorderTraversal(TreeNode *root) { 21 // write your code here 22 vector<int> result; 23 if (root == NULL) { 24 return result; 25 } 26 stack<TreeNode *> sta; 27 TreeNode *cur = root; 28 while (cur!=NULL || !sta.empty()) { 29 while (cur != NULL) { 30 result.insert(result.end(), cur->val); 31 sta.push(cur); 32 cur = cur->left; 33 } 34 cur = sta.top(); 35 sta.pop(); 36 cur = cur->right; 37 } 38 return result; 39 } 40 };