Leetcode::Construct Binary Tree from Inorder and Postorder 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 *build( vector<int>&inorder, vector<int> &postorder,int in_s,int in_e, int pos_s, int pos_e)
{
if( in_s >= in_e )
{
return NULL;
}

int val = postorder[pos_e-1];

TreeNode * tmp=new TreeNode(val);

int i;

for(i=in_s; i< in_e ; i++ )
{
if( val == inorder[i])
{
break;
}
}

int len = i - in_s;

tmp->left=build(inorder,postorder,in_s,i,pos_s ,pos_s + len);
tmp->right=build(inorder,postorder,i+1,in_e,pos_s+len,pos_e -1);
return tmp;
}
TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
return build(inorder,postorder,0,inorder.size(),0,postorder.size());
}
};