Construct Binary Tree from Preorder and Inorder Traversal

 1 class Solution {
 2 public:
 3     TreeNode *buildTree( vector<int> &preorder, vector<int> &inorder ) {
 4         if( preorder.empty() || preorder.size() != inorder.size() ) { return 0; }
 5         return BuildSub( preorder, 0, preorder.size()-1, inorder, 0, inorder.size()-1 );
 6     }
 7 private:
 8     TreeNode *BuildSub( vector<int> &preorder, int preStart, int preEnd, vector<int> &inorder, int inStart, int inEnd ) {
 9         if( inStart > inEnd ) { return 0; }
10         int index = 0;
11         while( inorder[inStart+index] != preorder[preStart] ) { ++index; }
12         TreeNode *treeNode = new TreeNode( preorder[preStart] );
13         treeNode->left = BuildSub( preorder, preStart+1, preStart+index, inorder, inStart, inStart+index-1 );
14         treeNode->right = BuildSub( preorder, preStart+index+1, preEnd, inorder, inStart+index+1, inEnd );
15         return treeNode;
16     }
17 };