由先序和中序重建二叉树

/**
 * 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* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
        if(pre.empty()||vin.empty()||pre.size()!=vin.size())
            return nullptr;
         
        return reConstructBinaryTreeCore(pre,0,pre.size()-1,vin,0,vin.size()-1);
    }
    TreeNode *reConstructBinaryTreeCore(vector<int> pre,int preStart,int preEnd,
                                        vector<int> vin,int vinStart,int vinEnd)
    {
        if(preStart>preEnd||vinStart>vinEnd)
            return nullptr;
        
        TreeNode *root=new TreeNode(pre[preStart]);
        for(int i=vinStart;i<=vinEnd;++i)
        {
            if(pre[preStart]==vin[i])
            {
                root->left=reConstructBinaryTreeCore(pre,preStart+1,preStart+i-vinStart,vin,vinStart,i-1);
                root->right=reConstructBinaryTreeCore(pre,preStart+i-vinStart+1,preEnd,vin,i+1,vinEnd);
                break;
            }
        }
        return root;
    }
};