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@shachopin/

Binary Tree Upside Down

Java

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  • Main.java
  • jdt.ls-java-project
Main.java
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class Main {
  public static void main(String[] args) {
    System.out.println("Hello world!");
  }
}

MySolution on lintcode 649 Binary Tree Upside Down
/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */

public class Solution {
    /**
     * @param root: the root of binary tree
     * @return: new root
     */
    public TreeNode upsideDownBinaryTree(TreeNode root) {
        // write your code here
        if (root == null) {
            return null;
        }
        if (root.left == null) {
            return root;
        }
        TreeNode newRoot = upsideDownBinaryTree(root.left); //每一层的newRoot其实都指向同一个reference
        root.left.left = root.right;
        root.left.right = root;
        root.left = null;
        root.right = null;
        return newRoot;
    }
}

==============================================

official solution:

// public class Solution {
//     /**
//      * @param root the root of binary tree
//      * @return the new root
//      */
     
//     TreeNode dfs(TreeNode cur) {
//         if (cur.left == null) {
//             return cur;
//         }
//         TreeNode newRoot = dfs(cur.left);
//         cur.left.right = cur;
//         cur.left.left = cur.right;
//         cur.left = null;            // important
//         cur.right = null;
//         return newRoot;
//     }

//     public TreeNode upsideDownBinaryTree(TreeNode root) {
//         // Write your code here
//         if (root == null) {
//             return null;
//         }
//         return dfs(root);
//     }
// }