[leetcode] Symmetric Tree－－二叉树遍历的应用

Posted 2020-06-22 lxydo

题目：

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

    1
   /   2   2
 / \ / 3  4 4  3
But the following is not:
    1
   /   2   2
   \      3    3

分析：
题目是要判断左右两颗子树是否对称，采用只要根节点的值相同，并且左边子树的左子树和右边子树饿右子树对称 且 左边子树的右子树和右边子树的左子树对称。采用树的遍历的思想，递归的解决该问题。
代码：

class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        if(root==NULL||(root->left==NULL&&root->right==NULL))
            return true;
        return postorder(root->left,root->right);
    }
    bool postorder(TreeNode* p,TreeNode* q)
    {
        if(p&&q)
        {
            if(p->val!=q->val)
                return false;
            return postorder(p->left,q->right)&&postorder(p->right,q->left);

        }else if(p==NULL&&q==NULL)
            return true;
        else
            return false;
    }
};