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leetcode dfs Flatten Binary Tree to Linked List

Flatten Binary Tree to Linked List

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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

click to show hints.

Hints:

If you notice carefully in the flattened tree, each node‘s right child points to the next node of a pre-order traversal.





题意:把一棵二叉树变为链表,要求原地进行转变。
思路:dfs
可以注意到,在链表表示中,每个节点的下一个节点是二叉树的先序遍历中的下一个节点,所以问题就转换为先序遍历了。
复杂度:时间O(n),空间O(log n)



TreeNode *cur;
void flatten(TreeNode *root) {
	if(!root) return;
	TreeNode *left = root->left;
	TreeNode *right = root->right;
	if(cur){
		cur->left = NULL;
		cur->right = root;
	}
	cur = root;
	flatten(left);
	flatten(right);
}



leetcode dfs Flatten Binary Tree to Linked List