symmetric-tree

/**
 * Given a binary tree, check whether it is a mirror of itself
 * (ie, symmetric around its center).
 *     1
 *    / \
 *   2   2
 *  / \ / \
 * 3  4 4  3
 *
 * 对于二叉树，检查它是否是自身的镜像（即，围绕其中心对称）。
 * 例如，此二叉树是对称的：
 *     1
 *    / \
 *   2   2
 *  / \ / \
 * 3  4 4  3
 */

/**
 * Given a binary tree, check whether it is a mirror of itself
 * (ie, symmetric around its center).
 *     1
 *    / \
 *   2   2
 *  / \ / \
 * 3  4 4  3
 *
 * 对于二叉树，检查它是否是自身的镜像（即，围绕其中心对称）。
 * 例如，此二叉树是对称的：
 *     1
 *    / \
 *   2   2
 *  / \ / \
 * 3  4 4  3
 */

public class Main42 {
    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(2);
        root.left.left = new TreeNode(3);
        root.right.right = new TreeNode(3);
        root.left.right = new TreeNode(5);
        root.right.left = new TreeNode(4);
        System.out.println(Main42.isSymmetric(root));
    }

    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) { val = x; }
    }

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

    public static boolean isEquals(TreeNode root1, TreeNode root2) {
        if (root1 == null && root2 == null) {
            return true;
        }
        if (root1 == null || root2 == null) {
            return false;
        }
        if (root1.val != root2.val) {
            return false;
        }
        return isEquals(root1.left, root2.right) && isEquals(root1.right, root2.left);
    }
}