114. Flatten Binary Tree to Linked List
Tags: ‘Tree’, ‘Depth-first Search’
Given a binary tree, flatten it to a linked list in-place.
For example, given the following tree:
1 / \ 2 5 / \ \ 3 4 6
The flattened tree should look like:
1
\
2
\
3
\
4
\
5
\
6
Solution
class Solution {
public void flatten(TreeNode root) {
flatten(root,null);
}
private TreeNode flatten(TreeNode root, TreeNode pre) {
if(root==null) return pre;
pre=flatten(root.right,pre);
pre=flatten(root.left,pre);
root.right=pre;
root.left=null;
pre=root;
return pre;
}
}
// straight
// O(n^2) NOT GOOD ENOUGH
// Right -> Left -> Root
class Solution {
public void flatten(TreeNode root) {
if (root == null) return;
TreeNode left = root.left, right = root.right;
root.left = null;
flatten(left);
flatten(right);
root.right = left;
TreeNode curr = root;
while (curr.right != null) {
curr = curr.right;
}
curr.right = right;
}
}