Leetcode Symmetric Tree 101

判断二叉树是否对称

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

1

/ \
2 2
/ \ / \
3 4 4 3
But the following is not:
1
/ \
2 2
\ \
3 3

/** 
 * 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; 
        else{ 
            return judge(root.left , root.right); 
        } 
    } 
    public boolean judge(TreeNode lchild,TreeNode rchild){ 
        if(lchild!=null && rchild!=null){ 
            return (lchild.val==rchild.val) && judge(lchild.left , rchild.right) && judge(lchild.right , rchild.left); 
        } 
        else if(lchild==null && rchild==null){ 
            return true; 
        } 
        else return false; 
    } 
}

递归