/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    
    public TreeNode reConstructBinaryTreeHelper(int[] pre,int pre_start,int pre_end,int[] in,int in_start,int in_end){
        
        if(pre_start > pre_end || in_start > in_end){
            return null;
        }
        
        TreeNode root = new TreeNode(pre[pre_start]);
        
        for(int i=in_start;i<=in_end;i++){
            
            //说明在中序中找到了根节点的位置
            if(pre[pre_start] == in[i]){
                root.left = reConstructBinaryTreeHelper(pre ,pre_start+1 , pre_start+i - in_start , in ,in_start , i-1 );
                root.right = reConstructBinaryTreeHelper(pre , pre_start + i - in_start + 1, pre_end , in , i +1 , in_end );
                break;
            }
            
        }
        return root;
    }
    
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        
        if(pre == null || in==null | pre.length!=in.length){
            return null;
        }
        
        return reConstructBinaryTreeHelper(pre,0,pre.length-1,in,0,in.length-1);
        
    }
}