重建二叉树-问题

1.QVector 代码-迭代器  {牛客网编不过    QT可以过}

TreeNode * reConstructBinaryTre2(QVector<int>::iterator startpre, QVector<int>::iterator endpre, QVector<int>::iterator startvin, QVector<int>::iterator endvin)
{
    TreeNode *root;
    root = new TreeNode(*startpre);//初始化

    if (startpre>endpre || startvin>endvin)//异常
    return NULL;

    QVector<int>::iterator it;
    //在中序遍历中寻找根节点位置

   for(it=startvin;it<=endvin;it++)
   {

    if(*it==*startpre)
    {
       int offset=it- startvin;
     root->left = reConstructBinaryTre2(startpre + 1, startpre + offset, startvin, it-1);
     root->right = reConstructBinaryTre2(startpre+offset + 1, endpre, it+1, endvin);
     break;
    }

   }
 return root;
}

TreeNode* reConstructBinaryTree(QVector<int> pre, QVector<int> vin)
{
  //做检查
   if(pre.empty()||vin.empty())
   {
       return NULL;
   }

    int size=pre.size();
    QVector<int>::iterator itpre=pre.begin(); //每一个迭代器对应一个容器  //和指针操作差不多  但不是指针
    QVector<int>::iterator itvin=vin.begin();

    TreeNode *root=reConstructBinaryTre2(itpre,itvin,itpre+size-1,itvin+size-1);

    return  root;

}


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QVector<int> pre1{ 1,2,4,7,3,5,6,8 };
    QVector<int> in1{ 4,7,2,1,5,3,8,6 };
    //        pre1.resize(100);
    //        in1.resize(100);
    //        cout << pre1.size() << endl;
    //        cout << in1.size() << endl;
    TreeNode * node;
    node = reConstructBinaryTree(pre1, in1);
    cout << node->val << endl;

   return a.exec();
}

2.只用QVector  {QT编不过  牛客可以过}

TreeNode* reConstructBinaryTree1(QVector<int> pre, int startpre, int endpre, QVector<int> vin, int startin, int endin)//主要在
{
    TreeNode *root;
    root = new TreeNode(pre[startpre]);//初始化

    if (startpre>endpre || startin>endin)//异常
        return NULL;


    for (int i = startin;i <= endin;i++)// 在中序遍历  中找根节点
    {
        if (vin[i] == pre[startpre])
        {
            root->left = reConstructBinaryTree1(pre, startpre + 1, startpre + i - startin, vin, startin, i - 1);

            root->right = reConstructBinaryTree1(pre, (i - startin) + startpre + 1, endpre, vin, i + 1, endin);

            break;
        }

    }

    return root;
}

TreeNode* reConstructBinaryTree(QVector<int> pre, QVector<int> vin)
{
  //做检查
   if(pre.empty()||vin.empty())
   {
       return NULL;
   }
    TreeNode * root = reConstructBinaryTree1(pre, 0, pre.size() - 1, vin, 0, vin.size() - 1);
    return  root;

}

3.李佳伟

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
#include <iostream>
using namespace std;
#include<vector>

 struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
    
};

class Solution {

public:
    TreeNode* construvt(vector<int>::iterator it1, vector<int>::iterator it2, vector<int>::iterator it3, vector<int>::iterator it4)
    {
        //if (!it1 || !it2 || !it3 || !it4)   //迭代器是类，不是指针
        //{
        //    return nullptr;
        //}
        int rootvalue = it1[0];   //获取根节点的值
        //创建一颗二叉树
        TreeNode*  pptree = new TreeNode(rootvalue); //构造函数初始化数据域
        pptree->val = rootvalue;  //可有可无
        pptree->left = nullptr;
        pptree->right = nullptr;
        
        vector<int>::iterator itt = it3;
        if (it1 == it2&&it3 == it4)
        {
            return pptree;
        }
        //在中序遍历中寻找根节点的位置
        while (itt <= it4&&itt[0] != rootvalue)
            itt++;
        //计算左子树和右子树所含节点的个数
        int leftnodenum = itt - it1;
        int rightnodenum = it4 - itt;

        //递归创建左子树
        if (leftnodenum>0)
        {
            pptree->left = construvt(it1 + 1, it1 + leftnodenum, it3, it3 + leftnodenum);
        }
        //递归创建右子树
        if (rightnodenum>0)
        {
            pptree->right = construvt(itt + 1 + leftnodenum, it2, itt + 1, it4);
        }
        return pptree;
    }

public:
    TreeNode* reConstructBinaryTree(vector<int> pre, vector<int> vin) {
        if(pre.empty() || vin.empty())
        {
            return nullptr;
        }
        int len = pre.size();
        vector<int>::iterator itpre = pre.begin();
        vector<int>::iterator itvin = vin.begin();
        return construvt(itpre, itpre + len - 1, itvin, itvin + len - 1);
    }
};