SymmetricTree.java

package binary_tree;

/**
 * @Author: Wenhang Chen
 * @Description:给定一个二叉树，检查它是否是镜像对称的。 例如，二叉树 [1,2,2,3,4,4,3] 是对称的。
 * <p>
 * 1
 * / \
 * 2   2
 * / \ / \
 * 3  4 4  3
 * 但是下面这个 [1,2,2,null,3,null,3] 则不是镜像对称的:
 * <p>
 * 1
 * / \
 * 2   2
 * \   \
 * 3    3
 * @Modified by:
 */
public class SymmetricTree {
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }

    public boolean isSymmetric(TreeNode root) {
        // 对于树的操作，传两个参数有时候会很方便
        return isMirror(root, root);
    }

    public boolean isMirror(TreeNode t1, TreeNode t2) {
        if (t1 == null && t2 == null) return true;
        if (t1 == null || t2 == null) return false;
        return (t1.val == t2.val)
                && isMirror(t1.right, t2.left)
                && isMirror(t1.left, t2.right);
    }
}