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
Note:
Bonus points if you could solve it both recursively and iteratively.
1 class Solution { 2 public boolean isSymmetric(TreeNode root) { 3 if(root ==null) return true; 4 return isSy(root.left,root.right); 5 } 6 public boolean isSy(TreeNode s,TreeNode t) { 7 if(s == null || t == null) return s==t; 8 9 if(s.val != t.val) return false; 10 11 return isSy(s.left,t.right) && isSy(s.right,t.left); 12 } 13 }