LeetCode-in-All
101. Symmetric Tree
Easy
Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).
Example 1:
Input: root = [1,2,2,3,4,4,3]
Output: true
Example 2:
Input: root = [1,2,2,null,3,null,3]
Output: false
Constraints:
- The number of nodes in the tree is in the range
[1, 1000]. -100 <= Node.val <= 100
Follow up: Could you solve it both recursively and iteratively?
Solution
/**
* Definition for a binary tree node.
* function TreeNode(val, left, right) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
*/
/**
* @param {TreeNode} root
* @return {boolean}
*/
var isSymmetric = function isSymmetric(root) {
if (!root) {
return true
}
return helper(root.left, root.right)
};
var helper = function(leftNode, rightNode) {
if (!leftNode || !rightNode) {
return leftNode === null && rightNode === null
}
if (leftNode.val !== rightNode.val) {
return false
}
return helper(leftNode.left, rightNode.right) && helper(leftNode.right, rightNode.left)
};
export { isSymmetric }