Construct Binary Tree from Preorder and Inorder Traversal

 1 public class Solution {
 2     public TreeNode buildTree(int[] preorder, int[] inorder) {
 3         TreeNode root;
 4         if(preorder.length == 0)
 5             return null;
 6         return createTree(preorder, inorder, 0, preorder.length - 1, 0, inorder.length - 1);
 7 
 8     }
 9     private TreeNode createTree(int[] preorder, int[] inorder, int preStart, int preEnd, int inStart ,int inEnd){
10         if(inStart > inEnd)
11             return null;
12         int value_root = preorder[preStart];                    //根据先序遍历第一个元素为根节点,找出根节点的值
13         int index = 0;                                            //根节点在中序遍历中的索引值
14         for(int i = inStart; i <= inEnd; i++){                    //查找根节点在中序遍历中的索引值
15             if(value_root == inorder[i]){
16                 index = i;
17                 break;
18             }
19         }//for
20         int length_leftTree = index - inStart;                    //左子树的长度
21         TreeNode root_left = createTree(preorder, inorder, preStart + 1, preStart + length_leftTree, inStart, index - 1);
22         TreeNode root_right = createTree(preorder, inorder, preStart + length_leftTree + 1, preEnd, index + 1, inEnd);
23         
24         TreeNode root = new TreeNode(value_root);
25         root.left = root_left;
26         root.right = root_right;
27         
28         return root;
29     }
30 }