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package com.usher.algorithm.offer;

/**

* @Author: Usher

* @Description:

* 对称的二叉树

* 判断一颗二叉树是不是对称的，如果一颗二叉树和它的镜像一样，那么就是对称的

*

*/

public class Solution28 {

boolean isSymmetrical(TreeNode pRoot) {

return pRoot == null || isEqual(pRoot.left, pRoot.right);

}

//先序遍历，递归实现。先判断根节点是否相等，然后在判断左右子树是否相等。

private boolean isEqual(TreeNode t1, TreeNode t2) {

if (t1 == null && t2 == null)

return true;

if (t2 == null || t1 == null)

return false;

//如果都不为空，则 需要比较左右子树后，再根据比较结果断定

return t1.val == t2.val && isEqual(t1.left, t2.right) && isEqual(t1.right, t2.left);

}

}