Invert Binary Tree

 

 

Invert a binary tree.

     4

   /   \

  2     7

 / \   / \

1   3 6   9

to

     4

   /   \

  7     2

 / \   / \

9   6 3   1

Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

呵呵

 

简单的bsf应用，我想我写的比较复杂，但是binary tree level traversal大法好

public class Solution {

    public TreeNode invertTree(TreeNode root) {

        if(root==null || (root.left==null&&root.right==null)) return root;

        LinkedList<TreeNode> q = new LinkedList<TreeNode>();

        

        int curNum =1, nextNum=0;

        q.add(root);

        while(!q.isEmpty()){

            curNum--;

            TreeNode n = q.poll();

            swapNodes(n);

            if(n.left!=null){

                q.add(n.left);

                nextNum++;

            }

            if(n.right!=null){

                q.add(n.right);

                nextNum++;

            }

            if(curNum==0){

                curNum = nextNum;

                nextNum=0;

            }

        }

        return root;

    }

    private void swapNodes(TreeNode n ){

        if(n==null||(n.left==null&&n.right==null)) return ;

        TreeNode tmp = n.right;

        n.right = n.left;

        n.left = tmp;

    }

}