[LintCode] Subtree

You have two every large binary trees: T1, with millions of nodes, and T2, with hundreds of nodes. Create an algorithm to decide if T2 is a subtree of T1.

Example

T2 is a subtree of T1 in the following case:

       1                3
      / \              / 
T1 = 2   3      T2 =  4
        /
       4

T2 isn't a subtree of T1 in the following case:

       1               3
      / \               \
T1 = 2   3       T2 =    4
        /
       4

Note

A tree T2 is a subtree of T1 if there exists a node n in T1 such that the subtree of n is identical to T2. That is, if you cut off the tree at node n, the two trees would be 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:
    bool isSame(TreeNode *T1, TreeNode *T2)
    {
        if(!T1 && !T2) return true;
        if((T1 && !T2) || (T2 && !T1))return false;
        if(T1->val != T2->val) return false;
        return isSame(T1->left, T2->left) && isSame(T1->right, T2->right);
    }
    bool isSubtree(TreeNode *T1, TreeNode *T2) {
        // write your code here
        
        if((T1 && !T2)|| (!T1 && !T2)) return true;
        if(!T1) return false;

        if(T1->val == T2->val
            && isSame(T1,T2)) return true;
        
        if(isSubtree(T1->left, T2)) return true;
        if(isSubtree(T1->right, T2)) return true;
        return false;
    }
};