Construct Binary Tree from Preorder and Inorder Traversal 前序和中序遍历构建二叉树

/**
 * 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* build(vector<int> &preorder,vector<int> &inorder,int pbegin,int pend,int ibegin,int iend)
{
TreeNode *root;
if(pbegin>pend||ibegin>iend||pend-pbegin!=iend-ibegin)
root= NULL;
else
{
root=new TreeNode(preorder[pbegin]);//注意！
int i=ibegin;
while(preorder[pbegin]!=inorder[i]&&i<inorder.size())
i++;
int left_len=i-ibegin;
  root->left=build(preorder,inorder,pbegin+1,pbegin+left_len,ibegin,i-1);
  root->right=build(preorder,inorder,pbegin+left_len+1,pend,i+1,iend);
    } 
    return root;
}
    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
        return build(preorder,inorder,0,preorder.size()-1,0,inorder.size()-1);
    }
};