题解 | #对称的二叉树#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    boolean res = true;
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param pRoot TreeNode类 
     * @return bool布尔型
     */
    public boolean isSymmetrical (TreeNode pRoot) {
        // write code here
        Deque<TreeNode> queue = new LinkedList<>();
        l2r(pRoot,queue);
        r2l(pRoot,queue);
        return res;
    }

    private void r2l(TreeNode pRoot, Deque<TreeNode> queue) {
        // TODO
        if(pRoot==null){
            return;
        }
        r2l(pRoot.right,queue);
        TreeNode cur = queue.poll();
        res = res && compare(cur,pRoot) && compare(cur.right,pRoot.left) && compare(cur.left,pRoot.right);
        r2l(pRoot.left,queue);
        
    }

    private boolean compare(TreeNode cur, TreeNode pRoot) {
        // TODO
        if(cur == null && pRoot == null){
            return true;
        }
        if(cur!=null && pRoot!=null && cur.val==pRoot.val){
            return true;
        }
        return false;
    }

    private void l2r(TreeNode pRoot, Deque<TreeNode> queue) {
        // TODO
        if(pRoot==null){
            return;
        }
        l2r(pRoot.left,queue);
        queue.add(pRoot);
        l2r(pRoot.right,queue);
        
    }
}