How to create interfaces for ADT's - interface

How do I create an interface for the following?
void push ( int value ) //adds value to list appropriately for a stack
int pop ( ) //remove and return value from list
boolean isEmpty() //returns true if the stack is empty
int size() //returns number of items in stack


postings nextPosition returns nul, freq returns 0, payload() returns null

I made simplest index with one document using LuceneTestCase. My goal is to write numbers to payload for each position of each term, that will be used in custom scoring formula implemented in custom Query/Scorer.
I used SimpleTextCodec and checked, that freq, positions and payload was really written to index.
But when I'm reading freq from the PostingEnum it returns 0, payload() returns null, nextPosition() throws an exception:
java.lang.AssertionError: got line=field model
at __randomizedtesting.SeedInfo.seed([D334C9D1B5C155E3:2AAE4BE5481F4C8F]:0)
org.apache.lucene.codecs.simpletext.SimpleTextFieldsReader$SimpleTextPostings Enum.nextPosition(
Here is how I'm reading the postings in the custom Query:
for (String field: fieldScores.keySet()) {
final Terms fieldTerms = reader.terms(field);
if (fieldTerms == null) {
if (!fieldTerms.hasPositions())
throw new IllegalStateException("Index does not contain positions");
if (!fieldTerms.hasPayloads())
throw new IllegalStateException("Index does not contain payloads");
final TermsEnum te = fieldTerms.iterator();
for (int j = 0; j < terms.length; j++) {
final Term t = terms[j];
if (t.field().equals(field) && te.seekExact(t.bytes())) {
PostingsEnum postingsEnum = te.postings(null, PostingsEnum.ALL);
int pos = postingsEnum.nextPosition();
BytesRef payload = postingsEnum.getPayload();
// assert payload.bytesEquals(new BytesRef(new byte[]{1}));
// TODO: use payload in scoring formula
fldScorers.add(new ConstTermScorer(this, t,
fieldScores.get(field) * termScores.get(t.text()),
I've found the reason. nextPosition(), freq() and payload() return 0 (or null) values because postingsEnum (iterator) is just created and not positioned on concrete document yet. postingsEnum.nextDoc() wasn't called and postingsEnum.docID() is -1. Stupid situation, but it would be better may be if nextPosition(), freq() and payload() would check postingsEnum.docID.

Get minimum value from list

I have a class ABC like this
public class ABC{
public int Id {get;set;}
public int UserCount {get;set;}
Now I add following records to a list of type ABC
List<ABC> lstABC = new List<ABC>();
lstABC.Add(new ABC(){Id=1,UserCount=5});
lstABC.Add(new ABC(){Id=2,UserCount=15});
lstABC.Add(new ABC(){Id=3,UserCount=3});
lstABC.Add(new ABC(){Id=4,UserCount=20});
I've another list of type int
List<int> lstIds = new List<int>();
Now i want to find out the minimum value of UserCount by comparing both the list where Id in lstABC should match the items presesnt in lstIds. I can get the minimum value of UserCount by using loops but is there any another way to get the value in an optimized way by avoiding loops?
You can use Enumerable.Join to link both lists:
var joined = from id in lstIds
join x in lstABC
on id equals x.Id
select x;
int minValue = joined.Min(x => x.UserCount);
This is more efficient than loops since Join uses a set to find matching items.
There's more than one way to skin a cat, this is a little bit less efficient:
int minValue = lstABC.Where(x => lstIds.Contains(x.ID)).Min(x => x.UserCount);
Try below code:
int min = lstABC.Min(entry => entry.UserCount);
var a = lstABC.Where(e => e.UserCount == min).FirstOrDefault();
var resul = lstIds.Where(e => e.Equals(a.Id)).FirstOrDefault();
var result = lstABC.Where(n =>n.Id == resul).FirstOrDefault();

Square Subsequence

A string is called a square string if it can be obtained by concatenating two copies of the same string. For example, "abab", "aa" are square strings, while "aaa", "abba" are not. Given a string, how many subsequences of the string are square strings? A subsequence of a string can be obtained by deleting zero or more characters from it, and maintaining the relative order of the remaining characters.The subsequence need not be unique.
eg string 'aaa' will have 3 square subsequences
Observation 1: The length of a square string is always even.
Observation 2: Every square subsequence of length 2n (n>1) is a combination of two shorter subsequences: one of length 2(n-1) and one of length 2.
First, find the subsequences of length two, i.e. the characters that occur twice or more in the string. We'll call these pairs. For each subsequence of length 2 (1 pair), remember the position of the first and last character in the sequence.
Now, suppose we have all subsequences of length 2(n-1), and we know for each where in the string the first and second part begins and ends. We can find sequences of length 2n by using observation 2:
Go through all the subsequences of length 2(n-1), and find all pairs where the first item in the pair lies between the last position of the first part and the first position of the second part, and the second item lies after the last position of the second part. Every time such a pair is found, combine it with the current subsequence of length 2(n-2) into a new subsequence of length 2n.
Repeat the last step until no more new square subsequences are found.
total_square_substrings <- 0
# Find every substring
for i in 1:length_of_string {
# Odd strings are not square, continue
if((length_of_string-i) % 2 == 1)
for j in 1:length_of_string {
# Remove i characters from the string, starting at character j
substring <- substr(string,0,j) + substr(string,j+1,length_of_string);
# Test all ways of splitting the substring into even, whole parts (e.g. if string is of length 15, this splits by 3 and 5)
SubstringTest: for(k in 2:(length_of_substring/2))
if(length_of_substring % k > 0)
first_partition <- substring[1:partition_size];
# Test every partition against the first for equality, if all pass, we have a square substring
for(m in 2:k)
if(first_partition != substring[(k-1)*partition_size:k*partition_size])
continue SubstringTest;
# We have a square substring, move on to next substring
break SubstringTest;
Here's a solution using LINQ:
IEnumerable<string> input = new[] {"a","a","a"};
// The next line assumes the existence of a "PowerSet" method for IEnumerable<T>.
// I'll provide my implementation of the method later.
IEnumerable<IEnumerable<string>> powerSet = input.PowerSet();
// Once you have the power set of all subsequences, select only those that are "square".
IEnumerable<IEnumerable<string>> squares = powerSet.Where(x => x.Take(x.Count()/2).SequenceEqual(x.Skip(x.Count()/2)));
And here is my PowerSet extension method, along with a "Choose" extension method that is required by PowerSet:
public static class CombinatorialExtensionMethods
public static IEnumerable<IEnumerable<T>> Choose<T>(this IEnumerable<T> seq, int k)
// Use "Select With Index" to create IEnumerable<anonymous type containing sequence values with indexes>
var indexedSeq = seq.Select((Value, Index) => new {Value, Index});
// Create k copies of the sequence to join
var sequences = Enumerable.Repeat(indexedSeq,k);
// Create IEnumerable<TypeOf(indexedSeq)> containing one empty sequence
/// To create an empty sequence of the same anonymous type as indexedSeq, allow the compiler to infer the type from a query expression
var emptySequence =
from item in indexedSeq
where false
select item;
var emptyProduct = Enumerable.Repeat(emptySequence,1);
// Select "Choose" permutations, using Index to order the items
var indexChoose = sequences.Aggregate(
(accumulator, sequence) =>
from accseq in accumulator
from item in sequence
where accseq.All(accitem => accitem.Index < item.Index)
select accseq.Concat(new[] { item }));
// Select just the Value from each permutation
IEnumerable<IEnumerable<T>> result =
from item in indexChoose
select item.Select((x) => x.Value);
return result;
public static IEnumerable<IEnumerable<T>> PowerSet<T>(this IEnumerable<T> seq)
IEnumerable<IEnumerable<T>> result = new[] { Enumerable.Empty<T>() };
for (int i=1; i<=seq.Count(); i++)
result = result.Concat(seq.Choose<T>(i));
return result;
I initially derive all possible sub-sequences and then i will check if the derived sub-sequence is a square sub-sequence or not
import java.util.*;
public class Subsequence {
static int count;
public static void print(String prefix, String remaining, int k) {
if (k == 0) {
if(prefix.length() %2 == 0 && check(prefix) != 0 && prefix.length() != 0)
if (remaining.length() == 0)
print(prefix + remaining.charAt(0), remaining.substring(1), k-1);
print(prefix, remaining.substring(1), k);
public static void main(String[] args)
//String s = "aaa";
Scanner sc = new Scanner(;
int t=Integer.parseInt(sc.nextLine());
count = 0;
String s = sc.nextLine();
for(int i=0;i<=s.length();i++)
public static int check(String s)
int i=0,j=(s.length())/2;
for(;i<(s.length())/2 && j < (s.length());i++,j++)
return 0;
return 1;
import java.util.*;
public class Solution {
Sample Input:
Sample Output:
public static void main(String[] args) {
//Creating an object of SquareString class
SquareString squareStringObject=new SquareString();
Scanner in = new Scanner(;
//Number of Test Cases
int T = in.nextInt();
String[] inputString=new String[T];
for(int i=0;i<T;i++){
// Taking input and storing in String Array
for(int i=0;i<T;i++){
//Calculating and printing the number of Square Strings
class SquareString{
//The counter maintained for keeping a count of Square Strings
private int squareStringCounter;
//Default Constructor initialising the counter as 0
public SquareString(){
//Function calculates and prints the number of square strings
public void numberOfSquareStrings(String inputString){
//Initialising the string part1 as a single character iterated over the length
for(int iterStr1=0;iterStr1<inputString.length()-1;iterStr1++){
String str1=""+inputString.charAt(iterStr1);
String str2=inputString.substring(iterStr1+1);
//Calling a recursive method to generate substring
//Recursive method to generate sub strings
private void generateSubstringAndCountSquareStrings(String str1,String str2){
for(int iterStr2=0;iterStr2<str2.length();iterStr2++){
String newStr1=str1+str2.charAt(iterStr2);
String newStr2=str2.substring(iterStr2+1);
private boolean isSquareString(String str){
return false;
String strPart1=str.substring(0,str.length()/2);
String strPart2=str.substring(str.length()/2);
return strPart1.equals(strPart2);

Constructor from scanner (Java)

public Note( Scanner input )
freq = input.nextInt();
The above code is in a separate file with everything it needs to run.
public void keyTyped( KeyEvent e )
char key = e.getKeyChar();
if( 'a' <= key && key <= 'y' )
// Ex5: put code here to add a new note to the list of notes
// in position current and increment current.
// Tip: key - 'a' will be an integer between 0 and 24,
// inclusive, corresponding to the desired note number when
// the user presses 'a' through 'x'
// Scanner input = new Scanner( );
---->// song.add( current, new Note( ? ));
// current++;
System.out.println(key - 'a');
I need to find a way to pass an int to a constructor that requires a Scanner. Please note that this in not the entire code but merely the code I thought would be required.
use int in Note constructor like this
public Note( int num )
freq = num;
then call it using input.nextInt() song.add( current, new Note(input.nextInt()
) );

cli::array<int> to iterator in c++-cli

I have managed class with function:
int DoSomething(cli::array<int>^ values) { .. }
In DoSomething I must call native function:
template <class It>
int Calculate(It beg, It end) {..}
Which iterator to use?
You'll want to use a pinning pointer to the managed array. This will fix the array in memory (i.e. make it so the garbage collector can't move it) and then you can treat it as a native array. Below is a sample using your methods.
Take note, that you need to finish using the array before the pinning pointer goes out of scope--once the pinning pointer goes out of scope, the managed array is no longer pinned, and the garbage collector is free to move the array.
Also, take note that pinning the first element of the array causes the entire managed array to be pinned (in general using a pinning pointer on one part of a managed object causes the entire managed object to be pinned).
template <class It> int Calculate(It beg, It end)
int sum = 0;
for (; beg != end; ++beg)
int i = *beg;
sum += i;
return sum;
int DoSomething(cli::array<int>^ values)
int numValues = values->Length;
pin_ptr<int> pNativeValuesBegin = &values[0];
int * pBegin = pNativeValuesBegin;
int * pEnd = pBegin + numValues;
return Calculate(pBegin, pEnd);
int main(array<System::String ^> ^args)
array<int> ^ values = gcnew array<int> { 1, 2, 3, 4, 5 };
int sum = DoSomething(values);
return 0;