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;
}
}