Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
1
/ \
2 2
/ \ / \
3 4 4 3
But the following [1,2,2,null,3,null,3] is not:
1
/ \
2 2
\ \
3 3
Solution:
/** * Definition for a binary tree node. * type TreeNode struct { * Val int * Left *TreeNode * Right *TreeNode * } */ func isSymmetric(root *TreeNode) bool { return isMirror(root, root) } func isMirror(left *TreeNode, right *TreeNode) bool { if left == nil && right == nil { return true } if left == nil || right == nil { return false } return left.Val == right.Val && isMirror(left.Left, right.Right) && isMirror(left.Right, right.Left) }