[leetcode]105. Construct Binary Tree from Preorder and Inorder Traversal

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/** * 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:    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {        int len=preorder.size();        if(len==0)            return {};        else            return build(preorder,inorder,0,len-1,0,len-1);    }    TreeNode* build(vector<int>& preorder, vector<int>& inorder,int preL,int preR,int inL,int inR)    {        if(preR<preL||inR<inL)            return {};                    TreeNode* root=new TreeNode(preorder[preL]);        if(preR==preL||inR==inL)            return root;                    int mid;        for(int i=inL;i<=inR;i++)        {            if(inorder[i]==preorder[preL])            {                mid=i;                break;            }        }        root->left=build(preorder,inorder,preL+1,preL+mid-inL,inL,mid-1);        root->right=build(preorder,inorder,preL+1+mid-inL,preR,mid+1,inR);        return root;            }};

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