Identical Binary Tree

题目：

Check if two binary trees are identical. Identical means the two binary trees have the same structure and every identical position has the same value.

分析：

想通了的话1分钟就可以做完

解法：

public class Solution {
    /**
     * @param a, b, the root of binary trees.
     * @return true if they are identical, or false.
     */

    public boolean isIdentical(TreeNode a, TreeNode b) {
        // Write your code here
        if (a == null && b == null) {
            return true;
        }

        if (a == null || b == null) {
            return false;
        }

        return a.val == b.val && isIdentical(a.left, b.left) && isIdentical(a.right, b.right);
    }
}