题目链接
101.对称二叉树
class Solution {public boolean check(TreeNode l, TreeNode r) {if (l == null && r == null)return true;if ((l == null && r != null) || (r == null && l != null))return false;if (l.val != r.val)return false;return check(l.left, r.right) && check(l.right, r.left);}public boolean isSymmetric(TreeNode root) {return check(root.left, root.right);}
}
小结：不能直接判断一个二叉树是否对称，于是想到判断其左右子树是否对称。
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