lintcode: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.

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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:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @aaram a, b, the root of binary trees.
     * @return true if they are identical, or false.
     */
    bool isIdentical(TreeNode* a, TreeNode* b) {
        // Write your code here
        
        if (a == NULL && b == NULL)
            return true;
        if (a == NULL || b == NULL)
            return false;
            
        if (a->val == b->val)
        {
            return isIdentical(a->left, b->left) && isIdentical(a->right, b->right);
        }
        return false;
    }
};