Identical Binary Tree

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.

Example

    1             1
   / \           / \
  2   2   and   2   2
 /             /
4             4

are identical.

    1             1
   / \           / \
  2   3   and   2   3
 /               \
4                 4

are not identical.

 /**
  * Definition of TreeNode:
  * public class TreeNode {
  *     public int val;
  *     public TreeNode left, right;
  *     public TreeNode(int val) {
  *         this.val = val;
  *         this.left = this.right = null;
  *     }
  * }
  */
 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) {
         if (a == null && b == null) return true;
         if (a == null || b == null) return false;

         if (a.val != b.val) return false;

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