Symmetric Tree

给一个二叉树, 看它左右两边是不是镜像的. 需要先观察一下镜像的概念, 就是翻转. 那么肯定需要递归的比较左右的node.

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