[TOC] ## 對稱二叉樹 給定一個二叉樹，檢查它是否是鏡像對稱的。 ``` 1 / \ 2 2 / \ / \ 3 4 4 3 ``` 解答 ``` /** * Definition for a binary tree node. * type TreeNode struct { * Val int * Left *TreeNode * Right *TreeNode * } */ func isSymmetric(root *TreeNode) bool { if root==nil{ return true } return helper(root.Left,root.Right) } func helper(left *TreeNode,right *TreeNode)bool{ if left==nil && right==nil{ return true } else if left==nil || right==nil || left.Val!=right.Val { return false } return helper(left.Left,right.Right) && helper(left.Right,right.Left) } ```