学步园

Flatten Binary Tree to Linked List

Oct 14 '12

7105 / 21371

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

其实就是前序遍历，还可以考虑非递归的方式

/**
 * 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;
            find(root);
    }
    
    public TreeNode find(TreeNode root){
        if(root==null) return null;
        TreeNode last =null;
        TreeNode left = root.left,right = root.right;
        if(root.left==null && root.right==null)  return root;
        if(root.left!=null){
            root.right = left;
            root.left = null;
            last = find(left);
            last.right = right;
        }
        if(right!=null)
           last = find(right);
        return last;
    }
}