题解 | #判断二叉树是否对称#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    public boolean isSymmetric (TreeNode root) {
        // write code here
        if(root == null) return true;
        Deque<TreeNode> d = new LinkedList<>();
        d.offerLast(root.left);
        d.offerLast(root.right);
        while(!d.isEmpty()){
            TreeNode left = d.pollFirst();
            TreeNode right = d.pollFirst();
            if(left == null && right == null) continue;
            if(left == null || right == null) return false;
            if(left.val != right.val) return false;
            d.offerLast(left.left);
            d.offerLast(right.right);
            d.offerLast(left.right);
            d.offerLast(right.left);
        }
        return true;
    }
}