/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
 
 
public class Solution {
    /**
     *@param preorder : A list of integers that preorder traversal of a tree
     *@param inorder : A list of integers that inorder traversal of a tree
     *@return : Root of a tree
     */
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        if(preorder.length==0||inorder.length==0){
            return null;
        }
        return bTree(preorder,0,preorder.length-1,inorder,0,inorder.length-1);
    }
    
    public TreeNode bTree(int []preorder,int i,int j,int []inorder,int k,int l){
        int index;
        TreeNode root=new TreeNode(preorder[i]);
        index=find(inorder,preorder[i]);
        if(i==j){
            return root;
        }
        if(index==k){
            root.left=null;
        }else{
            root.left=bTree(preorder,i+1,i+index-k,inorder,k,index-1);
        }
        if(index==l){
            root.right=null;
        }else{
            root.right=bTree(preorder,i+index-k+1,j,inorder,index+1,l);
        }
        
        return root;
    }
    
    
    public int find(int []arr,int k){
        for(int i=0;i<arr.length;i++){
            if(arr[i]==k){
                return i;
            }
        }        
        return -1;
    }
}