[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:
    void build(vector<int> &inorder, vector<int> &postorder, int l, int r, int index, TreeNode *&root) {
        if(l>r)
            return;
        root = new TreeNode(postorder[index]);
        int i;
        for(i=l;i<=r;i++) 
            if(inorder[i]==postorder[index]) 
                break;
        build(inorder, postorder, i+1, r, index-1, root->right);
        build(inorder, postorder, l, i-1, index-r+i-1, root->left); 
    }
    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
        if(inorder.size()==0)
            return NULL;
        TreeNode *root;
        build(inorder, postorder, 0, inorder.size()-1, postorder.size()-1, root);
        return root;
    }
};