leetcode 101 对称二叉树

简介

如何判断一颗对称二叉树, 最本质的特点就是左右子树是否相等. 递归遍历即可,注意终止条件的添加

code

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool check(TreeNode *p, TreeNode *q){
        if(!p && !q) return true;
        if(!p || !q) return false;
        return p->val == q->val && check(p->left, q->right) && check(p->right, q->left);
    }
    bool isSymmetric(TreeNode* root) {
        return check(root, root);
    }
};

class Solution {
    boolean check(TreeNode p, TreeNode q){
        if(p == null && q == null) return true;
        if(p == null || q == null) return false;
        return p.val == q.val && check(p.left, q.right) && check(p.right, q.left);
    }
    public boolean isSymmetric(TreeNode root) {
        return check(root, root);
    }
}