105. Construct Binary Tree from Preorder and Inorder Traversal

题目：

Given preorder and inorder traversal of a tree, construct the binary tree.

Note:

You may assume that duplicates do not exist in the tree.
解题思路：

/**
* 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) {
return buildTree_help(preorder,0,preorder.size()-1, inorder,0,inorder.size()-1);
}
TreeNode* buildTree_help(vector<int>& preorder,int start_pre,int end_pre, vector<int>& inorder,int start_in,int end_in){
if(start_pre>end_pre)return NULL;
TreeNode *root = new TreeNode(preorder[start_pre]);
int i = find(inorder.begin()+start_in,inorder.begin()+end_in,root->val) - inorder.begin()-start_in;
root->left = buildTree_help(preorder,start_pre+1,start_pre+i, inorder,start_in,start_in+i-1);
root->right = buildTree_help(preorder,start_pre+i+1,end_pre, inorder,start_in+i+1,end_in);
return root;
}
};