leetcode-101-Symmetric-Tree

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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:

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2
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4
5
    1
   / \
  2   2
 / \ / \
3  4 4  3

But the following is not:

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5
  1
 / \
2   2
 \   \
 3    3

分析

判断一颗二叉树是不是对称的。

解决方案1(C++)

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/**
 * 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 isSymmetric(TreeNode* root) {
        return root==NULL || isEqual(root->left, root->right);
    }

private:
    bool isEqual(TreeNode* left, TreeNode* right) {
        if(left!=NULL && right!=NULL && left->val == right->val) {
            return isEqual(left->left, right->right) && isEqual(left->right, right->left);
        }
        return left==NULL && right==NULL;
    }
};

解决方案2(Python)

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if not root:
            return True
        return self.isEqual(root.left, root.right)
        
    def isEqual(self, left, right):
        if left and right and left.val == right.val:
            return self.isEqual(left.left, right.right) and self.isEqual(left.right, right.left)
        return not left and not right

相关问题

题目来源