LeetCode(51) Symmetric Tree
阿新 • • 發佈:2019-01-12
題目描述
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree is symmetric:
But the following is not:
判斷一棵二叉樹是否對稱。
解題思路
根據題目要求,可以認為是樹的層序遍歷的一種應用。可以遞迴的判斷樹的左右子樹是否相等。
- 根節點直接遞迴判斷左右子樹即可;
- 對於根節點一下的結點,需要判斷
- 左結點的左子樹和右結點的右子樹;
- 左結點的右子樹和右結點的左子樹
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
bool isSame(TreeNode* left, TreeNode* right)
{
if (!left && !right) return true;
if(left && !right || !left && right) return false;
if(left->val != right->val) return false;
return isSame(left->left, right->right) && isSame(left->right, right->left);
}
bool isSymmetric(TreeNode* root) {
if (!root) return true;
return isSame(root->left, root->right);
}
};