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symmetric tree

admin 11月 13, 2020 0

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

But the following [1,2,2,null,3,null,3] is not:

1
2
3
4
5
 
  1
 / 
2   2
    
 3    3

Note:
Bonus points if you could solve it both recursively and iteratively.

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 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class  {
    public boolean isSymmetric(TreeNode root) {
        if(root==null) return true;
        return checkSymmetric(root.left,root.right);
    }
    
    public boolean checkSymmetric(TreeNode left,TreeNode right) {
        if(left==null || right==null) return left==right;
        if(left.val != right.val) return false;
        return checkSymmetric(left.left,right.right) && checkSymmetric(left.right,right.left);
    }
    
}
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