[Leetcode]Symmetric Tree
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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
判断一棵树是否为镜像对称的。
我的做法是:
把左子树按“根左右”的顺序遍历一遍,把沿途的数值记录下来(空值记为特殊符号'a')。
把右子树按“根右左”的顺序遍历一遍,把沿途的数值记录下来(空值记为特殊符号'a')。
看两个字符串相不相等。
class Solution {public: bool isSymmetric(TreeNode *root) { string leftFirst = ""; string rightFirst = ""; LRtraversal(root,leftFirst); RLtraversal(root,rightFirst); return leftFirst == rightFirst; }private: void LRtraversal(TreeNode *root, string& seq) { if(root==NULL) { seq+='a'; return; } seq += root->val + '0'; LRtraversal(root->left, seq); LRtraversal(root->right, seq); } void RLtraversal(TreeNode *root, string& seq) { if(root==NULL) { seq+='a'; return; } seq += root->val + '0'; RLtraversal(root->right, seq); RLtraversal(root->left, seq); }};
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