标签:
Same with inorder.
1. recursive:
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 void getTree(TreeNode *root, vector<int> &result) { 13 if (!root) return; 14 result.push_back(root->val); 15 getTree(root->left, result); 16 getTree(root->right, result); 17 } 18 vector<int> preorderTraversal(TreeNode *root) { 19 vector<int> result; 20 getTree(root, result); 21 return result; 22 } 23 };
2. directly use stack
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> result; 14 if (!root) return result; 15 stack<TreeNode *> s; 16 while (root || !s.empty()) { 17 if (root) { 18 s.push(root->right); 19 result.push_back(root->val); 20 root = root->left; 21 } else { 22 root = s.top(); 23 s.pop(); 24 } 25 } 26 return result; 27 } 28 };
3. two pointers:
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> result; 14 if (!root) return result; 15 TreeNode *prev = NULL; 16 while (root) { 17 result.push_back(root->val); 18 if (!root->left) { 19 root = root->right; 20 } else { 21 prev = root->left; 22 while(prev->right && prev->right != root) prev = prev->right; 23 if (!prev->right) { 24 prev->right = root; 25 root = root->left; 26 } else { 27 prev->right = NULL; 28 root = root->right; 29 result.pop_back(); 30 } 31 } 32 } 33 return result; 34 } 35 };
LeetCode – Refresh – Binary Tree Pre Order Traversal
标签:
原文地址:http://www.cnblogs.com/shuashuashua/p/4346193.html