[LeetCode] Flatten Binary Tree to Linked List

Total Accepted: 10982Total Submissions:40794My Submissions

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

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public void flatten(TreeNode root) {        if (root == null) return;                flatten(root.left);        flatten(root.right);                TreeNode node = root.left;                if (root.left != null) {            // get last node in left tree            while (node.right != null) node = node.right;            node.right = root.right;            root.right = root.left;            root.left = null;        }    }}

 

public class Solution {    // store current last node    private TreeNode last;    public void flatten(TreeNode root) {        if (root == null) return;                TreeNode tmp = root.right;                if (last == null) last = root;        else {            last.right = root;            last = root;        }        flatten(root.left);        flatten(tmp);                root.left = null;    }}

// without recursionpublic class Solution {    // store current last node    public void flatten(TreeNode root) {                while (root != null) {            if (root.left != null) {                // get bigest element in left tree                TreeNode p = root.left;                while (p.right != null) p = p.right;                p.right = root.right;                root.right = root.left;                root.left = null;            }                        root = root.right;        }    }}