101. Symmetric Tree

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public static boolean isMirror(TreeNode r, TreeNode l){
if( r == null && l == null) return true;
if( r == null && l != null) return false;
if( r != null && l == null) return false;
if (r.val != l.val) return false;
if (r.val == l.val)
return isMirror(l.right,r.left) && isMirror(l.left, r.right);
else return false;
}
public boolean isSymmetric(TreeNode root) {
if (root == null) return true;
return isMirror(root.right,root.left);
}
}

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