【LeetCode】101. Symmetric Tree
2017-06-16 15:31
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题目:
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree
But the following
题解:题目要求判断该树是不是对称的,要注意相比较的是左结点的右子树与右节点的左子树,而不是左子树与左子树相比较。判断是否是对称的临界条件,要找全,尤其是NULL的情况。
答案:
/**
* 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) {
if(root==NULL)
return 1;
return f(root->right,root->left);
}
bool f(TreeNode* r1,TreeNode* r2)
{
if(r1==NULL&&r2==NULL)
return 1;
else if(r1==NULL||r2==NULL)
return 0;
if(r1->val!=r2->val)
return 0;
return f(r1->right,r2->left)&&f(r1->left,r2->right);
}
};
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree
[1,2,2,3,4,4,3]is symmetric:
1 / \ 2 2 / \ / \ 3 4 4 3
But the following
[1,2,2,null,3,null,3]is not:
1 / \ 2 2 \ \ 3 3
题解:题目要求判断该树是不是对称的,要注意相比较的是左结点的右子树与右节点的左子树,而不是左子树与左子树相比较。判断是否是对称的临界条件,要找全,尤其是NULL的情况。
答案:
/**
* 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) {
if(root==NULL)
return 1;
return f(root->right,root->left);
}
bool f(TreeNode* r1,TreeNode* r2)
{
if(r1==NULL&&r2==NULL)
return 1;
else if(r1==NULL||r2==NULL)
return 0;
if(r1->val!=r2->val)
return 0;
return f(r1->right,r2->left)&&f(r1->left,r2->right);
}
};
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