从前序与中序遍历中构造二叉树---leetcode105题

给定两个整数数组 preorder 和 inorder ，其中 preorder 是二叉树的先序遍历， inorder 是同一棵树的中序遍历，请构造二叉树并返回其根节点。

class Solution {
public:
    TreeNode* traversal(vector& preorder, vector& inorder) {
        if(preorder.size() == 0) return NULL;

        int rootval = preorder[0];
        TreeNode* root = new TreeNode(rootval);

        if(preorder.size() == 1) return root;
        int deliminterIndex;
        for(deliminterIndex = 0; deliminterIndex < inorder.size(); deliminterIndex++){
            if(inorder[deliminterIndex] == rootval) break;
        }

        vector leftinorder(inorder.begin(), inorder.begin() + deliminterIndex);
        vector rightinorder(inorder.begin() + deliminterIndex + 1, inorder.end());

        vector leftpreorder(preorder.begin() + 1, preorder.begin()+leftinorder.size()+1);
        vector rightpreorder(preorder.begin()+leftinorder.size()+1,preorder.end());

        root->left = traversal(leftpreorder,leftinorder);
        root->right = traversal(rightpreorder,rightinorder);

        return root;
    }
    TreeNode* buildTree(vector& preorder, vector& inorder) {
        if(preorder.size() == 0 || inorder.size() == 0) return NULL;
        return traversal(preorder,inorder);    
    }
};