leetcode-Construct Binary Tree from Inorder and Postorder Traversal

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

这道题如果用递归来求解是不难的，只要根据二叉树中序和后续遍历的特点即可，不知道非递归该如何求解？

/** * 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.empty())            return NULL;        return buildTree(inorder, 0, inorder.size()-1, postorder, 0, postorder.size()-1);    }private:    TreeNode *buildTree(vector<int> &inorder, int istart, int iend,                      vector<int> &postorder, int pstart, int pend) {        if (istart == iend)            return new TreeNode(inorder[istart]);                int i;        for (i=istart; i<=iend; ++i) {            if (inorder[i]==postorder[pend]) {                break;            }        }                TreeNode *root = new TreeNode(inorder[i]);                if (i>istart)            root->left = buildTree(inorder, istart, i-1, postorder, pstart, pstart+i-istart-1);                if (i<iend)            root->right = buildTree(inorder, i+1, iend, postorder, pstart+i-istart, pend-1);                return root;    }    };