一、题目内容

二、题解

解法1：

思路

递归

代码

public class Solution {
    public boolean isSymmetric (TreeNode root) {
        // write code here
        return check(root,root);
    }
    public boolean check(TreeNode n1,TreeNode n2){
        if(n1 == null && n2 == null){
            return true;
        }
        if(n1==null||n2==null){
            return false;
        }
        return n1.val == n2.val && check(n1.left,n2.right) && check(n1.right,n2.left);
    }
}

解法2：

思路

迭代

代码

迭代法

public class Solution {
    public boolean isSymmetric (TreeNode root) {
        // write code here
        return check(root,root);
    }
    public boolean check(TreeNode n1,TreeNode n2){
        Stack<TreeNode> stack = new Stack<TreeNode>();
        stack.push(n1);
        stack.push(n2);
        while(!stack.isEmpty()){
            n1 = stack.pop();
            n2 = stack.pop();
            if (n1 == null && n2 == null) {
                continue;
            }
            if ((n1 == null || n2 == null) || n1.val != n2.val) {
                return false;
            }
            stack.push(n1.left);
            stack.push(n2.right);
            stack.push(n1.right);
            stack.push(n2.left);
        }
        return true;
    }
}