leetcode 101. Symmetric Tree
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree is symmetric:
1
/ \
2 2
/ \ / \
34 43
But the following is not:
1
/ \
2 2
\ \
3 3
Note:
Bonus points if you could solve it both recursively and iteratively.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean isSymmetric(TreeNode root) {
if(root == null) return true;
return helper(root.left, root. right) ;
}
public boolean helper(TreeNode left, TreeNode right){
if(left == null && right == null) return true;
if(left == null || right == null) return false;
if(left.val != right.val)
return false;
return helper(left.left,right.right) && helper(left.right, right.left);
}
}
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