前序遍历和中序遍历构造二叉树[lintcode]

/** * Definition of TreeNode: * class TreeNode { * public: *     int val; *     TreeNode *left, *right; *     TreeNode(int val) { *         this->val = val; *         this->left = this->right = NULL; *     } * } */class Solution {    /**     *@param preorder : A list of integers that preorder traversal of a tree     *@param inorder : A list of integers that inorder traversal of a tree     *@return : Root of a tree     */public:    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {        // write your code here        vector<int> pre_l,pre_r,in_l,in_r;//定义这四个变量来存储左右子树的前序和中序序列        TreeNode* root=NULL;         int i=0;        int index=0;        if(!preorder.empty()||!inorder.empty())//如果序列中不为空，继续构建        {            root=new TreeNode(preorder[0]);        for(i=0;i<inorder.size();i++)        {            if(preorder[0]==inorder[i])            {                index=i;//找出分割中序序列的分割点，左边为左子树的，右边为有子树的              break;            }        }        for(i=0;i<index;i++)//重新找出前面部分前中序列        {            pre_l.push_back(preorder[i+1]);            in_l.push_back(inorder[i]);        }        for(i=index+1;i<inorder.size();i++)//找出后面部分的前中序列        {            pre_r.push_back(preorder[i]);            in_r.push_back(inorder[i]);        }        //依次构建分割的部分，缩小区间，直至构建完        root->left=buildTree(pre_l,in_l);        root->right=buildTree(pre_r,in_r);        }        return root;    }};