27、二叉树的镜像

1、递归的方法

/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

public TreeNode(int val) {
this.val = val;

}

}
*/
public class Solution {
public void Mirror(TreeNode root) {
if(root == null) return;
TreeNode temp = root.left;
root.left = root.right;
root.right = temp;
Mirror(root.left);
Mirror(root.right);
}
}

2、循环的方法

import java.util.ArrayDeque;
/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

public TreeNode(int val) {
this.val = val;

}

}
*/
public class Solution {
public void Mirror(TreeNode root) {
if(root==null ) return;
ArrayDeque<TreeNode> stack = new ArrayDeque<TreeNode>();
//将根节点压入栈
stack.push(root);
while(!stack.isEmpty())
{
//弹出top节点并交换该结点的左右子树
TreeNode father = stack.pop();
TreeNode temp = father.left;
father.left = father.right;
father.right = temp;
//左子树不为空则压入栈
if(father.left!=null)
stack.push(father.left);
//右子树不为空则压入栈
if(father.right!=null)
stack.push(father.right);
}
}
}