Construct Binary Tree from Preorder and Inorder 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:    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {        if(preorder.empty() || inorder.empty()) return NULL;return buildTree(preorder,0,preorder.size()-1,inorder,0,inorder.size()-1);    }TreeNode *buildTree(const vector<int> &preorder,int preLeft,int preRight,const vector<int> &inorder,int inLeft,int inRight){if(preLeft>preRight || inLeft>inRight) return NULL;//根节点TreeNode *root=new TreeNode(preorder[preLeft]);//计算左子树结点数int i=0;for(i=inLeft;i<=inRight;i++){if(inorder[i]==preorder[preLeft]){break;}}const int leftSubTree=i-inLeft;root->left=buildTree(preorder,preLeft+1,preLeft+leftSubTree, inorder,inLeft,i-1);root->right=buildTree(preorder,preLeft+leftSubTree+1,preRight, inorder,i+1,inRight);return root;}};