題目鏈接

101.對稱二叉樹

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);}
}

小結：不能直接判斷一個二叉樹是否對稱，于是想到判斷其左右子樹是否對稱。