Develop Reference

Issues with Kattis "0-1 Sequences" Solution

Since last night I have been working very hard trying to write a solution to the problem "0-1 Sequences" (https://open.kattis.com/problems/sequences) on Kattis. At this point, I am at my wits end. I keep getting the wrong answer on the third test case, and I've tried everything I can possibly think of to fix my code. I'm fairly certain that the formula I am using to compute the result is correct, and I haven't been able to find an example where it gives the wrong answer. I suspect the issue is something to do with how I am calculating the modulus, but I've written and rewritten the relevant parts of the code and I am still failing each time. Below is my code (sorry in advance, I've been working like a madman with not much regard for writing "nice" code).
import java.util.*;
import java.util.ArrayList;
public class oneZeroSequences {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String s = sc.nextLine();
//leading zero's have no effect on the number of inversions,
//and we therefore get rid of them all right off the bat.
while(s.charAt(0)=='0'){
s=s.substring(1);
if(s.length()==0){
System.out.println(0);
System.exit(0);
}
}
System.out.println(findSum(s));
System.exit(0);
}
public static long findSum(String s) {
int m=1000000007;
long res = 0;
//if passed an empty string, the sum of inversions is obviously 0
if(s.length()==0){
return 0;
}
while(s.charAt(0)=='0'){
s=s.substring(1);
if(s.length()==0){
return 0;
}
}
//if the first character of the string is a question mark, we handle the case
//where that question mark is 1 first, and then remove the question mark since
//leading 0's have no effect on inversions.
while(s.charAt(0)=='?'){
res+=findSum("1"+s.substring(1))%m;
s=s.substring(1);
if(s.length()==0){
return res%m;
}
}
ArrayList<Integer> qArray = new ArrayList<Integer>();
int start=0;
int found;
//here we construct an array of the indices of question marks in the string
while(true){
found=s.indexOf('?', start);
if(found==-1){
break;
}
qArray.add(found);
start=found+1;
}
ArrayList<Integer> zeroArray = new ArrayList<Integer>();
start=0;
found=0;
//here we construct an array of the indices of 0's in the string
while(true){
found=s.indexOf('0', start);
if(found==-1){
break;
}
zeroArray.add(found);
start=found+1;
}
long k = qArray.size();
long a = zeroArray.size();
long zeroSum = sumArrayList(zeroArray);
long qSum = sumArrayList(qArray);
Double dres = 0.0;
//the formula for sum of inversions is as follows:
//2^k*(zeroSum) + 2^(k-1)*(qSum) - (a^2-a)*2^(k-1) - (2a-1)*2^(k-2) - (k^2+k)*2^(k-3)
//the following lines of code apply this formula, taking the modulus at each step.
if(k>=3){
res += (expBySquaringMod(2, k)*(zeroSum%m))%m;
//res=(res%m+m)%m;
res +=((expBySquaringMod(2, k-1))*(qSum%m))%m;
//res=(res%m+m)%m;
res -= ((((((a%m)*(a%m))%m)-a%m)%m)*expBySquaringMod(2,k-1))%m;
//res=(res%m+m)%m;
res -= (((((2*a-1)%m)*(k%m))%m)*expBySquaringMod(2,k-2))%m;
//res=(res%m+m)%m;
res-= (((((k%m)*(k%m))%m+k%m)%m)*expBySquaringMod(2, k-3))%m;
//res=(res%m+m)%m;
return res%m;
}
//the expBySquaringMod function will give incorrect
//results for negative exponents, hence the following code.
dres += ((Math.pow(2,k))*(zeroSum%m))%m;
dres=(dres%m+m)%m;
dres +=((Math.pow(2,k-1))*(qSum%m))%m;
dres=(dres%m+m)%m;
dres -= (((((a%m)*(a%m))%m-a%m)%m)*(Math.pow(2,k-1)))%m;
dres=(dres%m+m)%m;
dres -=((((2*a-1)%m*(k%m)%m)*(Math.pow(2,k-2))))%m;
dres=(dres%m+m)%m;
dres-=((((k%m)*(k%m)%m+k%m))%m*(Math.pow(2,k-3)))%m;
dres=(dres%m+m)%m;
res+=dres.intValue()%m;
return res%m;
}
public static int sumArrayList(ArrayList<Integer> list) {
int res = 0;
for(int d : list) {
res+=d;
}
return res;
}
//this function was written to deal with the massive powers of two required for the solution
public static long expBySquaringMod(int base, long exp) {
int m=1000000007;
long res=1;
if(exp%2==0) {
for(int i=0; i<exp/2;i++) {
res=(res*base*base)%m;
}
} else{
res=base;
for(int i=0; i<exp/2;i++) {
res=(res*base*base)%m;
}
}
return res;
}
}
Any help will be greatly appreciated. This problem has been causing me a lot of distress.

Problem with getting data to go into an array

So for this program, the mean and median are supposed to calculated and displayed but I do not think the data I am inputting is getting put into the array because it runs without error but does not display any data I have put into it.
public static double Mean(double[] gradeArray, int numGrades) {
double totalArray = 0.0;
double mean;
for (int i = 0; i < numGrades; i++) {
totalArray = gradeArray[i] + totalArray;
}
mean = totalArray / numGrades;
return mean;
}
public static double Median(double[] gradeArray, int numGrades) {
double median;
Arrays.sort(gradeArray, 0, numGrades);
if (numGrades % 2 == 0) {
median = ((gradeArray[(numGrades / 2)] + gradeArray[(numGrades / 2 + 1)]) / 2);
} else {
median = gradeArray[(numGrades / 2)];
}
return median;
}
private void Enter_Grades_ButtonActionPerformed(java.awt.event.ActionEvent evt) {
double[] totalArray = new double[25];
String text_box_input_str = null;
double text_box_input_num = 0;
int numGrades = 0;
String num_grades_str;
DecimalFormat df = new DecimalFormat("#0.0##");
do {
try {
text_box_input_str = JOptionPane.showInputDialog(null, "Enter Item Price", "Enter Price", JOptionPane.PLAIN_MESSAGE);
if (text_box_input_str == null || text_box_input_str.isEmpty()) {
return;
}
if (text_box_input_num > 0) {
double[] gradeArray = null;
gradeArray[numGrades] = text_box_input_num;
numGrades++;
num_grades_str = Integer.toString(numGrades);
num_grades_text.setText(num_grades_str);
Mean_Text.setText(df.format(Mean(gradeArray, numGrades)));
Median_Text.setText(df.format(Median(gradeArray, numGrades)));
}
} catch (NumberFormatException e) {
System.out.println("NumberFormatException caught");
JOptionPane.showMessageDialog(null, "You Must Input numeric data!", "Bad Data!", JOptionPane.ERROR_MESSAGE);
}
} while (text_box_input_str != null && !text_box_input_str.isEmpty());
}
I expect the program to calculate the data that is inputted and calculate the mean and median and then display the totals

it looks like text_box_input_num is set to 0, never updated, but then there is an if check if it's > 0

Rather than pointing out the problem with your code directly, I'll give some pointers on how to find it yourself.
break your code down into smaller parts
for each part, write both the method and the tests that prove the method does what you expect
once the individual parts are working, write the method (and tests) that use them.
You'll end up with several methods with names like getValues, hasValue, printError, checkValidValue, showMedian etc. all of which do exactly what you want.
I guarantee that if you do that it'll become pretty clear very quickly what's wrong.

Generate Data Points for Graph from an equation

I don't want to solve an equation and my question is not about Graphs and Trees Data Structures. I am trying to generate Data Points for graph from an equation given by user. I want efficient algorithm, easy to use and easy to maintain data structures. I have two solutions in mind
1: This is trivial and I have seen in many Applications.
String expr = "2*x+3*x";
Evaluator evaluator = new Evaluator();//I have this class
for (int i = start; i < end; i += step)
{
evaluator.setConstant("x", i);
double ans = evaluator.evaluate(expr);
}
This is very slow because each time every step is repeated like tokenzing, verifying, conversion to RPN, preparing stacks and queues and at last result calculation. The possible solution to this problem is somehow caching all stacks and queues but after that a comparison would be required between current expression and previous expression to use last stored state.
2: Currently I am developing second solution. The purpose of this is efficiency and would be used in Symbolic calculation in future.
So far my implementation
Variable.java
import java.text.DecimalFormat;
public class Variable
{
private final double pow;
private final double coefficient;
private final String symbol;
public Variable(String symbol)
{
this.symbol = symbol;
this.pow = 1.0;
this.coefficient = 1.0;
}
public Variable(String symbol, double coefficient, double pow)throws IllegalArgumentException
{
if (coefficient == 0.0)throw new IllegalArgumentException("trying to create variable with coefficient 0");
if (pow == 0.0)throw new IllegalArgumentException("trying to create variable with exponent 0");
this.symbol = symbol;
this.pow = pow;
this.coefficient = coefficient;
}
public final String getSymbol()
{
return this.symbol;
}
public final double getPow()
{
return this.pow;
}
public final double getCoefficient()
{
return this.coefficient;
}
#Override
public String toString()
{
StringBuilder builder = new StringBuilder();
DecimalFormat decimalFormat = new DecimalFormat("#.############");
if (coefficient != 1.0)builder.append(decimalFormat.format(this.coefficient));
builder.append(this.symbol);
if (this.pow != 1.0)builder.append("^").append(decimalFormat.format(this.pow));
return builder.toString();
}
/*
* Stub Method
* Generate some unique hash code
* such that chances of key collision
* become less and easy to identify
* variables with same power and same
* symbol*/
#Override
public int hashCode()
{
return 0;
}
}
Equation.java
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
public class Equation
{
private final ArrayList<Boolean> operations;
private final HashMap<String, Variable> variableHashMap;
private int typesOfVariables;
public Equation(Variable variable)
{
this.variableHashMap = new HashMap<>();
this.operations = new ArrayList<>();
this.typesOfVariables = 1;
this.variableHashMap.put(variable.getSymbol(), variable);
}
/*Stub Method*/
public void addVariable(Variable variable, boolean multiply)
{
/*
* Currently not covering many cases
* 1: Add two variables which have same name
* and same pow.
* 2: variable which are wrapped inside functions e.g sin(x)
* and many other.*/
if (multiply && variableHashMap.containsKey(variable.getSymbol()))
{
Variable var = variableHashMap.get(variable.getSymbol());
Variable newVar = new Variable(var.getSymbol(), var.getCoefficient() * variable.getCoefficient(), var.getPow() + variable.getPow());
/*
* Collision chances for variables with same name but
* with different powers*/
this.variableHashMap.replace(var.getSymbol(), newVar);
}
else
{
++this.typesOfVariables;
this.variableHashMap.put(variable.getSymbol(), variable);
}
this.operations.add(multiply);
}
/*Stub Method
*Value for every variable at any point will be different*/
public double solveFor(double x)
{
if (typesOfVariables > 1)throw new IllegalArgumentException("provide values for all variables");
Iterator<HashMap.Entry<String, Variable>> entryIterator = this.variableHashMap.entrySet().iterator();
Variable var;
double ans = 0.0;
if (entryIterator.hasNext())
{
var = entryIterator.next().getValue();
ans = var.getCoefficient() * Math.pow(x, var.getPow());
}
for (int i = 0; entryIterator.hasNext(); i++)
{
var = entryIterator.next().getValue();
if (this.operations.get(i))ans *= var.getCoefficient() * Math.pow(x, var.getPow());
else ans += var.getCoefficient() * Math.pow(x, var.getPow());
}
return ans;
}
#Override
public String toString()
{
StringBuilder builder = new StringBuilder();
Iterator<HashMap.Entry<String, Variable>> entryIterator = this.variableHashMap.entrySet().iterator();
if (entryIterator.hasNext())builder.append(entryIterator.next().getValue().toString());
Variable var;
for (int i = 0; entryIterator.hasNext(); i++)
{
var = entryIterator.next().getValue();
if (this.operations.get(i))builder.append("*").append(var.toString());
else builder.append(var.toString());
}
return builder.toString();
}
}
Main.java
class Main
{
public static void main(String[] args)
{
try
{
long t1 = System.nanoTime();
Variable variable = new Variable("x");
Variable variable1 = new Variable("x", -2.0, 1.0);
Variable variable2 = new Variable("x", 3.0, 4.0);
Equation equation = new Equation(variable);
equation.addVariable(variable1, true);//2x+x
equation.addVariable(variable2, true);
for (int i = 0; i < 1000000; i++)equation.solveFor(i);//Calculate Million Data Points
long t2 = System.nanoTime();
System.out.println((t2-t1)/1000/1000);
System.out.println(equation.toString());
}
catch (Exception e)
{
System.out.println("Error: " + e.getMessage());
}
}
}
Am I going in right direction?
Is there any commonly used Algorithm for this problem?
My main goal is efficiency, code cleanness and code maintainability.
Note: I am not native English speaker so please ignore any grammatical mistake.
Thanks.

I do not see any problem with your first code. Yes may be at every step your code "repeat like tokenzing, verifying, conversion to RPN, preparing stacks and queues and at last result calculation", but in the end all of this is just linear number of steps. So I fail to see how it can make it really slow.
One of the biggest screens I have seen was 2560x1440 pixels, which means that most of the time you would need less than 2500 points to draw your graph there.
If you point is code cleanness and code maintainability, then most probably a code consisting of 5 lines is better than the code consisting of 200.

Several errors keep occurring in eclipse

I'm trying to write a program that opens a txt file and display information from that txt file. Java is my first language, and I'm taking java as a second language class since there's no beginning java class in my school. I'm struggling with this code for about an week. Any little help would be helpful. Appreciate for your help.
It keeps saying :
Exception in thread "main"java.lang.ArrayIndexOutOfBoundsException:6
at store.Franchise.<init>(Franchise.java:10)
at store.FileIO.readData(FileIO.java:10)
at store.Driver.main(Driver.java:9)
Here is what I've got:
Sample txt file:
Day1 Day2 Day3 Day4 Day5
2541.56 2258.96 2214 2256 2154
2041.56 1758.96 1714 1756 1654
3041.56 2758.96 2714 2756 2654
3563.54 3280.94 3235.98 3277.98 3175.98
2547.21 2264.61 2219.65 2261.65 2159.65
4040.55 3757.95 3712.99 3754.99 3652.99
Store.java:
package store;
import java.io.IOException;
public class Store {
private float salesByWeek[][];
public Store() {
salesByWeek = new float[5][7];
// assign the array value at index 5, t to salesByWeek
}
public void setSaleForWeekDayIntersection(int week, int day, float sale) {
salesByWeek[week][day] = sale;
// store the sale value to SalesByWeek array at the index pointed to by week, day
// for exaample, it can be week 2 and day 3 (Wednesday)
}
float[] getSalesForEntireWeek(int week) {
// this will find the total sales for the whole week - all 5 days or 7 days including week ends Saturday and Sunday
float[] sales = new float[7];
// declare an array of type float and of size 7 - name the array as sales
for (int d = 0; d < 7; d++)
{
sales[d] = salesByWeek[week][d];
// the index d runs from 0 to 7
}
return sales;
}
float getSaleForWeekDayIntersection(int week, int day) {
return salesByWeek[week][day];
// the return value is the arraycontent pointed to by index week and day
}
float getTotalSalesForWeek(int week) {
float total = 0;
for (int d = 0; d < 7; d++)
{
total += salesByWeek[week][d];
// increment total by adding the array content salesByWeek at index week, d ( if d is the day)
}
return total;
// send the value of total back to the caller function
}
float getAverageSalesForWeek(int week) {
return getTotalSalesForWeek(week) / 7;
// divide the total sales for the whole week by 7 so that we get the average sales and return it
}
float getTotalSalesForAllWeeks() {
float total = 0; // declare a total variable of type float and initialize to 0 ( zero)
for (int w = 0; w < 5; w++)
{
total += getTotalSalesForWeek(w);
// sum up the total for the whole week and store it to the total variable
}
return total;
// return the sum computed above
}
float getAverageWeeklySales() {
return getTotalSalesForAllWeeks() / 5;
// AVERAGE for 5 days - just Monday to Friday only - excludes the week ends
}
int getWeekWithHighestSaleAmount() {
// top performing sales in the whole week
int maxWeek = 0;
float maxSale = -1;
for (int w = 0; w < 5; w++)
// run the for loop from 0 to 5 in steps of 1
{
float sale = getTotalSalesForWeek(w);
// first store the total sales in to the sale variable of type float
if (sale > maxSale)
{ // if at all if we find any amount greater than the max sale then replace max sale with the new sale amount
// and also note down the contributor - in the sense that which w ( week) achieved top sales
maxSale = sale;
maxWeek = w;
}
}
return maxWeek;
}
int getWeekWithLowestSaleAmount() {
int minWeek = 0;
float minSale = Float.MAX_VALUE;
for (int w = 0; w < 5; w++)
{
float sale = getTotalSalesForWeek(w);
if (sale < minSale)
{
minSale = sale;
minWeek = w;
}
}
// comments are same as the top sales except in reverse order
// first store an arbitary minimum sale figure
// then compare each running week's vaue with the lowest
// if at all when we encounter any value lower than the preset value then replace it
return minWeek;
// finally return the minimum value in that week
}
public void analyzeResults() {
for (int w = 0; w < 5; w++) // run the for loop from 0 to 5
{
System.out.printf("---- Week %d ----\n", w); // print a title decoration
System.out.printf(" Total sales: %.2f\n", getTotalSalesForWeek(w)); // display or print out the total sales summed earlier in called function
System.out.printf(" Average sales: %.2f\n", getAverageSalesForWeek(w)); // display the average sales figure
}
System.out.printf("\n");
System.out.printf("Total sales for all weeks: %.2f\n", getTotalSalesForAllWeeks()); // print sum of the sales for the entire week
System.out.printf("Average weekly sales: %.2f\n", getAverageWeeklySales()); // print weekly average sales
System.out.printf("Week with highest sale: %d\n", getWeekWithHighestSaleAmount()); // print highest performing or top sales
System.out.printf("Week with lowest sale: %d\n", getWeekWithLowestSaleAmount()); // print lowest sales or the struggling week
}
public void setsaleforweekdayintersection(int week, int day, float f) {
}
}
Franchise.java:
package store;
public class Franchise {
private Store stores[];
public Franchise(int num) { // now for a franchise store
stores = new Store[num]; // instantiate an array object of type class Store
// the class is Store
// the objects are named as stores
for(int i=0; i<=num; i++) stores[i] = new Store();
}
public Store getStores(int i) { // GETTER display or return values
return stores[i];
}
public void setStores(Store stores, int i) { // setter assign values
this.stores[i] = stores;
}
}
FileIO.java:
package store;
import java.io.*;
import java.util.StringTokenizer;
public class FileIO {
// Franchise readData(String filename)
Franchise readData(String filename, int numstores) {
Franchise f1 = new Franchise(numstores);
boolean DEBUG = true;
int ctr = 0;
// open the file
// read the line
// parse the line - get one value
// and set it in the correct location in 2 d array
try {
FileReader file = new FileReader(filename); // file is equivalent to a file pointer in c/c++
BufferedReader buff = new BufferedReader(file); // buffered reader will read a chunk in to the variable buff
boolean eof = false;
while (!eof) {
String line = buff.readLine();
ctr++;
if (line == null)
eof = true;
else {
if (DEBUG)
System.out.println(line);
if (ctr > 1) {
StringTokenizer a = new StringTokenizer(line);
for (int week = 0; week < 5; week++) {
for (int day = 0; day < 7; day++) {
String l = a.nextToken();
float f = Float.parseFloat(l); // parseFloat will store to variable f of type float
f1.getStores(ctr - 2)
.setsaleforweekdayintersection(week,
day, f);
if (DEBUG)
System.out.print("f" + f + " ");
}
}
}
}
}
} catch (IOException f2) {
}
return f1;
}
}
Driver.java:
package store;
public class Driver
{
public static void main(String[] args)
{
FileIO readdata = new FileIO();
Franchise f1 = readdata.readData("E:/Files/Salesdat.txt", 6);
System.out.println("Data read");
}
}
DriverImpl.java ( I got no idea why I need this subclass, but my tutor told me that I need this):
package store;
public class DriverImpl extends Driver {
}

I would like to change the line 10 in Franchise.java to
for(int i=0; i<num; i++) stores[i] = new Store();
Notice I removed the <= and put an = instead. Whenever dealing with array indices, one should always use the < comparator with the size as a good practice.

Valid indexes in an array are 0 to length - 1. Change <= to < like,
stores = new Store[num];
// the class is Store
// the objects are named as stores
for(int i=0; i<num; i++) stores[i] = new Store(); //stores[num] is invalid.

jList output everything on one line

I have created a program for calculating the interest on given values. But when i calculate it, the output on the jList comes out in one line, 10 times.
Can anyone help me, and tell me why this happens :)?
From my calculate class
public ArrayList<String> calculateInterest(double years, double principal, double amount)
{
ArrayList<String> results = new ArrayList<>();
for (years = 1; years <= 10; years++)
{
amount = principal * Math.pow(rate + 1, years);
String amountToString = "" + amount;
results.add(amountToString);
}
return results;
}
´
From my GUI (Under the button)
double aar = Double.parseDouble(txtAntalAar.getText());
double belob = Double.parseDouble(txtBelob.getText());
double rente = Double.parseDouble(txtRente.getText());
ArrayList output = cal.calculateInterest(aar, belob, rente);
for (int i = 0; i < output.size(); i++)
{
myListModel.add(i, output);
}
I have also tried with:
for (String s : cal.calculateInterest(aar, rente, rente))
{
myListModel.addElement(output);
}
But same issue. Here is a photo of the output - I what them to switch line between each number:

You are adding the whole list instead of the element. Use
for (int i = 0; i < output.size(); i++)
myListModel.add(i, output.get(i));

That's because you are adding the entire ArrayList and not de item.
for (String s : cal.calculateInterest(aar, rente, rente))
{
//myListModel.addElement(output); this way you add the entire array
myListModel.addElement(s); // now you add only the item
}