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;
    }
}