/**

  * Definition for binary tree

  * public class TreeNode {

  *     int val;

  *     TreeNode left;

  *     TreeNode right;

  *     TreeNode(int x) { val = x; }

  * }

  */

 public class Solution {

     public TreeNode buildTree(int[] preorder, int[] inorder) {

         // bug 3: consider when length is 0.

         if (preorder == null || inorder == null || preorder.length == 0 || preorder.length != inorder.length) {

             return null;

         }

         // bug 4: end index is length - 1.

         return buildTree(preorder, inorder, 0, preorder.length - 1, 0, preorder.length - 1);

     }

     public TreeNode buildTree(int[] preorder, int[] inorder, int preStart, int preEnd, int inStart, int inEnd) {

         // base case;

         if (preStart > preEnd) {

             return null;

         }

         int rootVal = preorder[preStart];

         TreeNode root = new TreeNode(rootVal);

         int pos = findTarget(inorder, rootVal, inStart, inEnd);

         // bug 5: left number is pos - instart can't add 1

         int leftNum = pos - inStart;

         root.left = buildTree(preorder, inorder, preStart + 1, preStart + leftNum, inStart, pos - 1);

         root.right = buildTree(preorder, inorder, preStart + leftNum + 1, preEnd, pos + 1, inEnd);

         return root;

     }

     // bug 1: return type required.

     // bug 2: this is not a bst. can't use binary search.

     public int findTarget(int[] A, int target, int start, int end) {

         for (int i = start; i <= end; i++) {

             if (target == A[i]) {

                 return i;

             }

         }

         return -1;

     }

 }