Solution.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        return build(preorder, inorder,0,preorder.length-1,0,inorder.length-1);
    }
    public TreeNode build(int[] preorder, int[] inorder,int ps,int pe,int is,int ie){
        if(ps>pe){
            return null;
        }
        int val=preorder[ps];
        TreeNode node=new TreeNode(val);
        int i = is;
        for (; i <=ie; i++) {
            if (inorder[i]==val) {
                break;
            }
        }
        int rang=i-is;
        node.left=build(preorder, inorder,ps+1,ps+rang,is,i-1);
        node.right=build(preorder,inorder,ps+rang+1,pe,i+1,ie);
        return node;
        
    }
}