【Construct Binary Tree from Inorder and Postorder Traversal】cpp

/**
 * Definition for a binary tree node.
 * 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()==0 || postorder.size()==0 ) return NULL;
        return Solution::buildTreeIP(inorder, 0, inorder.size()-1, postorder, 0, postorder.size()-1);
    }
    static TreeNode* buildTreeIP(
        vector<int>& inorder, 
        int bI, int eI, 
        vector<int>& postorder, 
        int bP, int eP )
    {
        if ( bI > eI ) return NULL;
        TreeNode *root = new TreeNode(postorder[eP]);
        int rootPosInorder = bI;
        for ( int i = bI; i <= eI; ++i )
        {
            if ( inorder[i]==root->val ) { rootPosInorder=i; break; }
        }
        int leftSize = rootPosInorder - bI;
        int rightSize = eI - rootPosInorder;
        root->left = Solution::buildTreeIP(inorder, bI, rootPosInorder-1, postorder, bP, bP+leftSize-1);
        root->right = Solution::buildTreeIP(inorder, rootPosInorder+1, eI, postorder, eP-rightSize, eP-1);
        return root;
    }
};