18. The reconstruction of a binary tree

 

 

 

class Solution {
public:
    TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
        int vinlen=vin.size();
        if(vinlen==0) 
            return NULL;
        vector<int> pre_left, pre_right, vin_left, vin_right;
  
        TreeNode* head = new TreeNode(pre[0]);
    
        int gen = 0;
        for(int i=0;i<vinlen;i++)
        {
            if(vin[i]==pre[0]) 
            {
                gen=i;
                break;
            }
        }
     
        for(int i=0;i<gen;i++)
        {
            vin_left.push_back (VIN [I]); // preorder traversal sequence left subtree 
            pre_left.push_back (pre [I + . 1 ]); // preorder traversal sequence before the left subtree 
        }
    
        for(int i=gen+1;i< vinlen;i++)
        {
             vin_right.push_back (VIN [I]); // preorder traversal sequence right subtree 
             pre_right.push_back (pre [I]); // preorder traversal sequence before the right subtree 
        }

         head->left = reConstructBinaryTree(pre_left, vin_left);
         head->right = reConstructBinaryTree(pre_right, vin_right);
         return head;        

    }
};