重建二叉树

题目描述

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

  
         root->left=reConstructBinaryTree(preleft,inleft);
        root->right=reConstructBinaryTree(preright,inright);
         return root;
    }
};/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    struct TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> in) {
        if (pre.empty() || in.empty() || pre.size()!=in.size()){
            return NULL;
        }
       TreeNode* root=new TreeNode(pre[0]);
        int len=in.size();
        int i,k=-1;
        vector<int>  preleft,preright,inleft,inright;
        for(i=0;i<len;i++)
            {
             if(pre[0]==in[i])
                      {
                        k=i;
                        break;
                      } 
        }
        if(k==-1)
             return NULL;
        
        for(i=0;i<len;i++)
            {
              if(i<k)
                   inleft.push_back(in[i]);
              if(i>k)
                  inright.push_back(in[i]);
        }
       k=inleft.size()+1;
         for(i=1;i<pre.size();i++)
           if(i<k)
               preleft.push_back(pre[i]);
             else
                preright.push_back(pre[i]);