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 3 4 5 | 1 / \ 2 2 / \ / \ 3 4 4 3 |
But the following [1,2,2,null,3,null,3] is not:
1 2 3 4 5 | 1 / \ 2 2 \ \ 3 3 |
Solution:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | /** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public boolean isSymmetric(TreeNode root) { if(root==null) return true; return isMirror(root.left,root.right); } public boolean isMirror(TreeNode p, TreeNode q) { if(p==null && q==null) return true; if(p==null || q==null) return false; return (p.val==q.val) && isMirror(p.left,q.right) && isMirror(p.right,q.left); } } } |
