Construct Binary Tree from Preorder and Inorder Traversal.java

/**
 * 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) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(preorder.length==0 || inorder.length==0) return null; 
        return buildTree(inorder, 0, inorder.length-1, preorder, 0, preorder.length-1); 
    }
    TreeNode buildTree(int [] inorder, int startI, int endI, int[] preorder, int startP, int endP)
    {
        if(startI>endI || startP>endP) return null; 
        if(startI==endI) return new TreeNode(inorder[startI]);
        if(startP==endP) return new TreeNode(preorder[startP]);
        int indexIn=findOrder(startI, endI, inorder, preorder[startP]); 
        if(indexIn==-1) return null; 
        TreeNode root=new TreeNode(inorder[indexIn]);
        root.left= buildTree(inorder, startI, indexIn-1, preorder, startP+1, indexIn-startI+startP );
        root.right= buildTree(inorder, indexIn+1, endI, preorder, indexIn-startI+startP+1, endP );
        return root; 
    }
    int findOrder(int start, int end, int [] inorder, int target)
    {
        for(int i=start; i<=end; i++)
        {
            if(inorder[i]==target) return i; 
        }
        return -1; 
    }
}