101. 对称二叉树

101. 对称二叉树

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

package com.test;

/**
 * @Author stono
 * @Date 2018/8/27 上午9:11
 */
public class Lesson101 {
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(1);
        TreeNode t2L = new TreeNode(2);
        TreeNode t2R = new TreeNode(2);
        TreeNode t3_1 = new TreeNode(3);
        TreeNode t3_2 = new TreeNode(4);
        TreeNode t3_3 = new TreeNode(4);
        TreeNode t3_4 = new TreeNode(3);
        t1.left = t2L;
        t1.right = t2R;
        t2L.left = t3_1;
        t2L.right = t3_2;
        t2R.left = t3_3;
        t2R.right = t3_4;
        boolean symmetric = isSymmetric(t1);
        System.out.println(symmetric);
    }

    public static boolean isSymmetric(TreeNode root) {
        if (root == null) {
            return true;
        }
        return isSymmetric(root.left, root.right);
    }

    private static boolean isSymmetric(TreeNode left, TreeNode right) {
        if (left == null && right == null) {
            return true;
        }
        if (left != null && right == null) {
            return false;
        }
        if (left == null && right != null) {
            return false;
        }
        if (left.val - right.val != 0) {
            return false;
        }
        return isSymmetric(left.left, right.right) && isSymmetric(left.right, right.left);
    }
}