leetcode 13:symmetric tree
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
Note:
Bonus points if you could solve it both recursively and iteratively.
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: bool isSymRec(TreeNode *left, TreeNode * right){ if(left == NULL && right==NULL){ return true; } else if(left == NULL || right == NULL) { return false; } return ( left->val == right->val && isSymRec( left->left, right->right) && isSymRec( left->right, right->left) ); //both are not NULL. } bool isSymmetric(TreeNode *root) { // Start typing your C/C++ solution below // DO NOT write int main() function if(root == NULL) return true; return isSymRec( root->left, root->right); } };
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public boolean isSymmetric(TreeNode root) { // Start typing your Java solution below // DO NOT write main() function if(root==null) { return true; } return isSysRec(root.left, root.right); } private boolean isSysRec(TreeNode left, TreeNode right){ if(left==null && right==null) { return true; } else if( left==null || right==null) { return false; } return (left.val==right.val) && isSysRec(left.left, right.right) && isSysRec(left.right, right.left); } }