Solution.java

package _101;


import structure.TreeNode;

import java.util.LinkedList;

/**
 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2017/10/09
 *     desc  :
 * </pre>
 */
public class Solution {
//    public boolean isSymmetric(TreeNode root) {
//        return root == null || helper(root.left, root.right);
//    }
//
//    private boolean helper(TreeNode left, TreeNode right) {
//        if (left == null || right == null) return left == right;
//        if (left.val != right.val) return false;
//        return helper(left.left, right.right) && helper(left.right, right.left);
//    }

    public boolean isSymmetric(TreeNode root) {
        if (root == null) return true;
        LinkedList<TreeNode> q = new LinkedList<>();
        q.add(root.left);
        q.add(root.right);
        TreeNode left, right;
        while (q.size() > 1) {
            left = q.pop();
            right = q.pop();
            if (left == null && right == null) continue;
            if (left == null || right == null) return false;
            if (left.val != right.val) return false;
            q.add(left.left);
            q.add(right.right);
            q.add(left.right);
            q.add(right.left);
        }
        return true;
    }

    public static void main(String[] args) {
        Solution solution = new Solution();
        System.out.println(solution.isSymmetric(TreeNode.createTestData("[1,2,2,3,4,4,3]")));
        System.out.println(solution.isSymmetric(TreeNode.createTestData("[1,2,2,null,3,null,3]")));
        System.out.println(solution.isSymmetric(TreeNode.createTestData("[9,-42,-42,null,76,76,null,null,13,null,13]")));
    }
}