[面试真题] LeetCode:Flatten Binary Tree to Linked List
Given a binary tree, flatten it to a linked list in-place.
For example, Given
1 / \ 2 5 / \ \ 3 4 6
The flattened tree should look like:
1 \ 2 \ 3 \ 4 \ 5 \ 6
Hints: If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.
解法 1:非递归解法
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 flatten(TreeNode *root) { 13 // Start typing your C/C++ solution below 14 // DO NOT write int main() function 15 if(NULL == root){ 16 return; 17 } 18 stack<TreeNode*> s; 19 TreeNode *p = root; 20 s.push(root); 21 while(p->left){ 22 s.push(p->left); 23 p = p->left; 24 } 25 while(s.size()){ 26 TreeNode *cur = s.top(); 27 s.pop(); 28 if(cur->right){ 29 p->left = cur->right; 30 cur->right = NULL; 31 while(p->left){ 32 s.push(p->left); 33 p = p->left; 34 } 35 } 36 } 37 p = root; 38 while(p->left){ 39 p->right = p->left; 40 p->left = NULL; 41 p = p->right; 42 } 43 } 44 };
Run Status: Accepted!
Program Runtime: 44 milli secs