[leetcode] 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.

/**
 * 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) {
         int len=preorder.length;
         if(len==0) 
             return null;
             
         TreeNode root=new TreeNode(preorder[0]);
         if(len==1) 
            return root;
            
         int index=0;
         for(int i=0;i<inorder.length;i++){
             if(inorder[i]==preorder[0]){
                 index=i;
                 break;
             }
         }
         if(index>0){
              int []preleft=new int[index];
              int []inleft=new int[index];
              System.arraycopy(preorder,1,preleft,0,index);
              System.arraycopy(inorder,0,inleft,0,index);
              root.left=buildTree(preleft,inleft);
         }
         if(len-index-1>0){
              int []preright=new int [len-index-1];
              System.arraycopy(preorder,index+1,preright,0,len-index-1);  
              int []inright=new int [len-index-1];
              System.arraycopy(inorder,index+1,inright,0,len-index-1);  
              root.right=buildTree(preright,inright);
         }
        
         return root;
    }
}