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.

public void flatten(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        TreeNode runner = root;
        while(runner!=null){
            if(runner.left!=null){
                findRightMostChild(runner.left).right = runner.right;
                runner.right = runner.left;
                runner.left = null;
            }
            runner = runner.right;
        }
        
    }
    
    public TreeNode findRightMostChild(TreeNode node){
        while(node.right!=null){
            node = node.right;
        }
        return node;
    }
FacebookTwitterGoogle+Share