【LeetCode】Symmetric Tree 判断一棵树是否是镜像的

题目：Symmetric Tree

<span style="font-size:18px;">/**LeetCode Symmetric Tree 对称的树
 * 思路：判断一棵树是否对称，1.有左子树就要有右子树
 * 						2.除根节点外对称节点值要相同
 * 注意：对称后就是左子树的左节点和右子树的右节点比较
	 * Definition for binary tree
	 * public class TreeNode {
	 *     int val;
	 *     TreeNode left;
	 *     TreeNode right;
	 *     TreeNode(int x) { val = x; }
	 * }
	 */
package javaTrain;

public class Train8 {
	    public boolean isSymmetric(TreeNode root) {
	    	if(root == null) return true;
	    	if(root.left == null && root.right == null) return true;
	    	else if(root.left == null || root.right == null) return false;
	    	return help(root.left,root.right);
	    }
	    private boolean help(TreeNode left,TreeNode right){
	    	if(left == null && right == null) return true;
	    	else if(left == null || right == null) return false;
	    	if(left.val == right.val)
	    		return help(left.left,right.right ) && help(left.right,right.left);
	    	else return false;
	    }
}
</span>