[Leetcode] Construct binary tree from preorder and inorder travesal 利用前序和中续遍历构造二叉树

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) 
13     {
14         int len=preorder.size();
15         return build(preorder,0,len-1,inorder,0,len-1);    
16     }
17 
18     TreeNode *build(vector<int> &preorder,int preBeg,int preEnd,vector<int> &inorder,int inBeg,int inEnd)
19     {
20         if(preBeg>preEnd||inBeg>inEnd)  return NULL;
21         TreeNode *root=new TreeNode(preorder[preBeg]);
22 
23         for(int i=0;i<inorder.size();++i)
24         {
25             if(inorder[i]==preorder[preBeg])
26             {
27                 root->left=build(preorder,preBeg+1,preBeg+i-inBeg,inorder,inBeg,i-1);
28                 root->right=build(preorder,preBeg+i+1-inBeg,preEnd,inorder,i+1,inEnd);
29             }
30         }
31         return root;
32     }
33 };