leetcode 101. symmetric tree

101. Symmetric Tree

Difficulty: Easy

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:

But the following [1,2,2,null,3,null,3] is not:

Note:
Bonus points if you could solve it both recursively and iteratively.

Solution

Language: Java


 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class  {
    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;
        }
        return left.val == right.val && helper(left.left, right.right) && helper(left.right, right.left);
    }
}

leetcode 101. symmetric tree

101. Symmetric Tree

Solution

近期文章

近期评论

标签

热门

文章归档

分类目录

功能