PROBLEM DESCRIPTION: Symmetric Binary Tree
Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).
SOLUTION
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class Solution {
public boolean isSymmetric(TreeNode root) {
if(root == null) return false;
return isSym(root.left, root.right);
}
public boolean isSym(TreeNode left, TreeNode right){
if(left == null && right == null){
return true;
} else if(left == null && right != null){
return false;
} else if(left != null && right == null){
return false;
}
if (left.val != right.val){
return false;
}
return isSym(left.left, right.right) && isSym(left.right, right.left);
}
}
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/