C++ 代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    unordered_map<int,int> pos;
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {

        //第一次没ac出来，难受
        for(size_t i=0;i<inorder.size();i++){
            //这个记录的是该值
            pos[inorder[i]]=i;
        }
       return reBuildTree(  preorder,  inorder,0,preorder.size()-1,0,preorder.size()-1);
    }

     TreeNode* reBuildTree( vector<int>& preorder, vector<int>& inorder,int pb,int pe,int is,int ie){
         if(pb>pe){
             return NULL;
         }
         TreeNode* root=new TreeNode(preorder[pb]);
         int len=pos[preorder[pb]]-is;
         root->left=reBuildTree(  preorder,  inorder,pb+1,pb+len,is,pos[preorder[pb]]-1);
         root->right=reBuildTree(  preorder,  inorder,pb+len+1,pe,pos[preorder[pb]]+1,ie);
         return root;
     }
};