LeetCode101----对称二叉树

给定一个二叉树，检查它是否是镜像对称的。

例如，二叉树 [1,2,2,3,4,4,3] 是对称的。

    1
   / \
  2   2
 / \ / \
3  4 4  3

但是下面这个 [1,2,2,null,3,null,3] 则不是镜像对称的:

    1
   / \
  2   2
   \   \
   3    3

代码如下：

public class LeetCode101 {
	public boolean isSymmetric = true;

	public static class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;

		TreeNode(int x) {
			val = x;
		}
	}

	public boolean isSymmetric(TreeNode root) {
		if (root == null) {
			return true;
		}
		isSymmetric(root.left, root.right);
		return isSymmetric;
	}

	public void isSymmetric(TreeNode left, TreeNode right) {
		if (left == null || right == null) {
			if (left != right) {
				isSymmetric = false;
			}
			return;
		}
		isSymmetric(left.left, right.right);
		isSymmetric(left.right, right.left);
		if (left != null && right != null) {
			if (left.val != right.val) {
				isSymmetric = false;
			}
		}
	}
}