• leetcode 101 Symmetric Tree ----- java


    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
    

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

    判断一棵树是否是对称的。

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

     也可以使用队列来解决这个问题。

     
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  • 原文地址:https://www.cnblogs.com/xiaoba1203/p/5997931.html
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