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 *buildTree(vector<int> &inorder, vector<int> &postorder) {
if( inorder.size() != postorder.size())
return NULL;
return core( inorder, 0, inorder.size()-1, postorder, 0, postorder.size()-1);
}
TreeNode *core( vector< int> &inorder, int left, int right, vector< int> &postorder, int start, int end){
if( left > right || start > end)
return NULL;
TreeNode *root = new TreeNode( postorder[end]);
int i = left;
for( ; i <= right; ++i){
if( inorder[i] == postorder[end])
break;
}
root->left = core( inorder, left, i-1, postorder, start, start+(i-left)-1);//这里要用下标减left，算offset。不然会数组越界
root->right = core( inorder, i+1, right, postorder, start+(i-left), end-1);//这里要用下标减left。算offset，不然会数组越界
return root;
}
};