import java.util.*;

public class MinimalBST {
    
     public int buildMinimalBST(int[] vals) {
         if(vals == null || vals.length <1)
            return 0;
         return buildMinimalBSTCore(vals, 0 , vals.length-1);
     }
    public int buildMinimalBSTCore(int[] vals, int start, int end) {

        if(end < start)
            return 0;
        int mid = (start + end)/2;
        int leftH = 1 + buildMinimalBSTCore(vals, start, mid-1);
        int rightH = 1 + buildMinimalBSTCore(vals, mid+1, end);
        
        return Math.max(leftH, rightH);
    }
}