Construct Binary Tree from Inorder and Postorder Traversal

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