Construct Binary Tree from Preorder and Inorder Traversal

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if(preorder.size()==0)
return NULL;
return build(preorder,inorder,0,preorder.size(),0);
}

TreeNode *build(vector<int> &preorder, vector<int> &inorder,int p,int t,int i)
{
if(t==0)
return NULL;
TreeNode* head = (TreeNode *)malloc(sizeof(TreeNode));
head->val = preorder[p];
int j = -1;
for( j = i;j<t+i;j++)
{
if(inorder[j] == preorder[p])
break;
}
head->left = build(preorder,inorder,p+1,j-i,i);
head->right = build(preorder,inorder,p+j-i,t-j-i,j+1);
return head;
}
};