114. 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

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.

 

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/**
 * Definition for a binary tree node.
 * 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;
        
        TreeNode c = root;
        while(c != null)
        {
            if(c.left != null)
            {
                TreeNode rightBranch = c.right;
                TreeNode leftBranch = c.left;
                c.left = null;
                c.right = leftBranch;
                
                TreeNode lastRight = c;
                while(lastRight.right != null)
                {
                    lastRight = lastRight.right;
                }
                lastRight.right = rightBranch;
            }
            c = c.right;
        }
    }
}