题目
请实现一个函数，用来判断一棵二叉树是不是对称的。如果一棵二叉树和它的镜像一样，那么它是对称的。
实现
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public class {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public (int val) {
this.val = val;
}
}
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public boolean isSymmetrical(TreeNode pRoot) {
if (pRoot == null)
return true;
return isSymmetricalHelper(pRoot.left, pRoot.right);
}
private boolean isSymmetricalHelper(TreeNode left, TreeNode right) {
if (left == null && right == null)
return true;
else if (left == null || right == null)
return false;
else if (left.val != right.val)
return false;
return isSymmetricalHelper(left.left, right.right) && isSymmetricalHelper(left.right, right.left);
}
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