LeetCode 101. Symmetric Tree

分析

难度 易

来源

https://leetcode.com/problems/symmetric-tree/

题目

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.

解答

Runtime: 8 ms, faster than 98.44% of Java online submissions for Symmetric Tree.

package LeetCode;

public class L101_SymmetricTree {
    public boolean isAlike(TreeNode p, TreeNode q) {//把一棵树的对称转化为两棵树的相似
        if(p==null&&q==null)
            return true;
        if((p==null&&q!=null)||(p!=null&&q==null)||(p.val!=q.val))
            return false;
        return isAlike(p.left,q.right)&&isAlike(p.right,q.left);
    }
    public boolean isSymmetric(TreeNode root) {
        if(root==null)
            return true;
        return isAlike(root.left,root.right);
    }
}