I want to know how recursive method work to prints a large X composed of smaller X's with a given “width”, input number, which is guaranteed to be odd.
the “width” is length (number) of X’s along one line large X.
Example for an X of width input number =3
the method will print this shape!
X X
X
X X
I try to solve this problem but I couldn't
can anyone here help me ..
in java code ,
This is my code he works good but prints wrong when numberinput=7 or 5
public static String shape(String i,int numberinput) {
//error check, not working for even numbers
if(numberinput%2 == 0)
return null;
//terminating condition, stop recursion when this occurs.
if(numberinput == 1)
return "X";
else
return "X"+" "+i+"\n" +" "+shape(" "+i,numberinput-2)+" "+"\n"+i+" "+"X";
}
he prints this when numberinput=5
X X
X X
X
X X
X X
A valid recursive method should have two parts.
Recursive call (call itself to do part of work)
Terminating condition (A condition to stop the recursion)
You have a recursive call, but not a termination condition. Hence your recursion won't stop until it fills up the entire stack and cause an exception. Hence you should include a terminating condition in your recursive method.
A sample implementation might look like this.
public static String shap(String i, int numberinput) {
//error check, not working for even numbers
if(numberinput%2 == 0)
return null;
//terminating condition, stop recursion when this occurs.
if(numberinput == 1)
return "X";
//recursion, call recursive until terminating condition occurs.
return "X" + i + shap(i, numberinput-2) + i + "X";
}
I have written a java code, in which recursion is only for the levels, to generate the string i have used a loop :
import java.util.*;
import java.lang.*;
import java.io.*;
public class Main
{
public static void main (String[] args) throws java.lang.Exception
{
List<String> ans = new ArrayList<String>();
shap(7, 1, ans);
//System.out.println(ans);
for(int i = 0;i < ans.size();i++){
System.out.println(ans.get(i));
}
}
public static void shap(int numberinput, int currentLevel, List<String> ans) {
if(currentLevel == numberinput+1) return;
String val = "";
for(int i = 1;i <= numberinput;i++){
if(i == currentLevel || i == (numberinput+1-currentLevel)) val += "X";
else val += " ";
}
ans.add(val);
shap(numberinput, currentLevel+1, ans);//Recursion step for the levels
}
}
Link to solution on Ideone : http://ideone.com/RioL9g
Related
Sorry I am having a mental block, can anyone see why I get the 'cannot convert from int to boolean' error message. Much appreciated
public static void main (String[]args) {
int max=10;
int sum=0;
int count=0;
for(int counter=0;counter=max-4;counter++) {
sum=max-4;
count=max-3;
for(sum=3;sum<5;sum++) {
if(count==0 && max>0){
System.out.println("Hello");
} else if (count<4) {
System.out.println("Go for it");
} else {
System.out.println("OK");
}
}
}
sum=sum+count;
System.out.println("Total = "+sum);
System.out.println("Max = "+count);
}
I feel like I have checked using the '==' for the if condition.
= is assignment, you need a comparison in the second term of your loop.
for(int counter=0;counter=max-4;counter++) {
should be
for (int counter = 0; counter < max - 4; counter++) {
(white space added, but note < is a comparison... perhaps you wanted <=).
In case of Java, the syntax of for loop is
for(initialization; Boolean_expression; update) {
// Statements
}
1) The initialization part executes only once when the flow enters the for loop for the first time
2) Next, the boolean expression is resolved according to the condition
3) Then next the update statement is resolved and after execution of the body of the for loop again the flow goes to the boolean expression and then update statement and the flow goes on.
So, In your program instead of a boolean expression, you have used an assignment operator which turns out to be 6 which is not 0 or 1. Boolean expression are true = 1 and false = 0. Hence the integer 6 cannot be converted to boolean. So, you can go with counter < max-4
I'm currently trying to use a function that compares the left and right side character to return a true or false Boolean value as to whether the string entered by the user is a palindrome or not, but I get a vague error statement to do with line 44. Not sure how to proceed. I am a beginner-level Java programmer who is open-minded and willing to learn, so don't roast me to hard haha.
import java.util.Scanner;
/**
*
* #author owner
*/
public class Q2_RecursivePalidrome {
public static void main(String[] args) {
int leftSideCharacter = 0;
int rightSideCharacter = 0;
Scanner scan = new Scanner (System.in);
System.out.println("Enter word to check whether palidrome: ");
String userInput = scan.next();
char[] checkPalidrome = userInput.toCharArray(); // creates an array of characters
System.out.println(isPalidrome(checkPalidrome, leftSideCharacter, rightSideCharacter));
}
public static boolean isPalidrome(char[] checkPalidrome, int leftSideCharacter, int rightSideCharacter) {
leftSideCharacter = 0;
rightSideCharacter = checkPalidrome.length - 1; // java arrays start at 0, not 1.
if (rightSideCharacter > leftSideCharacter) { // check both ends of string character by character
// to be palidrome, both sides of string should be same
//
if (checkPalidrome[leftSideCharacter] == checkPalidrome[rightSideCharacter]) {
return (isPalidrome(checkPalidrome, leftSideCharacter + 1, rightSideCharacter - 1));
}
else {
return false;
}
}
return true;
}
}
There are a couple main issues here, but you have the right idea:
Your recursive function uses left and right indices to determine which characters to compare in the test string. However, these two pointers are immediately set to the left and right ends of the string when the function is called, so they never recursively move towards the middle. Since the base case where the indices are equal is unreachable, the stack overflows. Remember, these calls are identical all the way down the stack, but with different parameters, so one-time "set up" tasks like setting initial indices should be moved outside of the recursive function.
Your initial pointer indices are 0, 0. This is an inaccurate "set up" call to the recursive function--it should be 0, string.length - 1.
Here is code that fixes these problems and cleans up comments and variable names:
import java.util.*;
public class Q2_RecursivePalidrome {
public static void main(String[] args) {
String test = "racecar";
System.out.println(isPalidrome(test.toCharArray(), 0, test.length() - 1));
}
static boolean isPalidrome(char[] test, int l, int r) {
if (l < r) {
if (test[l] == test[r]) {
return isPalidrome(test, l + 1, r - 1);
}
else {
return false;
}
}
return true;
}
}
By the way, the important lesson to take from all this is how to debug your program. In this case, printing your indices (the arguments that change from one call to the next) at the top of your recursive function will clearly show that they aren't doing what you expect.
import java.util.*;
class A{
static int count=0;
static String s;
public static void main(String z[]){
int n;
Scanner sc=new Scanner(System.in);
n=sc.nextInt();
System.out.println(noOfBouncy(n));
}
public static int noOfBouncy(int k){
int limit=(int)Math.pow(10,k);
s=new String("1");
int num=Integer.parseInt(s);
while(num<limit){
if(isIncreasing(s) || isDecreasing(s) ){
}
else{
count++;
}
num++;
s=new String(Integer.toString(Integer.parseInt(s)+1));
}
count=limit-count;
return count;
}
}
public static boolean isIncreasing(String s){
int len=s.length();
for(int i=0;i<len-1;i++){
if(s.charAt(i)>s.charAt(i+1)){
return false;
}
}
return true;
}
public static boolean isDecreasing(String s){
int len=s.length();
for(int i=0;i<len-1;i++){
if(s.charAt(i)<s.charAt(i+1)){
return false;
}
}
return true;
}
I have given the definitions to the two functions used isIncreasing() & isDecresing()
The program runs well for the value of n<7 but does not respond for values above it, Why ?
I accept the programming style is very immature,please ignore.
I've tried to execute it with n=7 and it finishes in 810ms, returning 30817.
However, I recommend to you to optimize the performance of your program by saving unnecessary object instantiation: It will be better if you maintain the counter in num, and convert it to string just once, at the beginning of the loop:
int num=1;
while (num < limit)
{
s=Integer.toString(num);
if (isIncreasing(s) || isDecreasing(s))
{
}
else
{
count++;
}
num++;
}
Like this it takes just 450ms to finish.
The program was not actually stuck but it is taking way too much time to complete its execution when value of 'n' is larger.
So now the question is, I need to optimize the code to take minimum time #Little have an optimization bit that's not enough.
Any hint would be appreciable.
To increase the performance you should avoid the conversation to String and do the check with numbers.
As it doesn't matter for the result if you start the comparison from left to right or from right to left one computational solution could be.
as pseudo code
1) compare the value of the right most digit with the digit on it's left
2) is it lower --> we found a decreasing pair
3) else check if it is bigger --> we found an increasing pair
4) else --> not a bouncy pair
5) if we found already one decreasing and one increasing pair it's bouncy number
6) divide the number by ten if it's bigger then ten repeat with step 1)
The method to check if it's a bouncy number could look like this
static boolean isBouncyNumber(int number) {
boolean increasingNumber = false;
boolean decreasingNumber = false;
int previousUnitPosition = number % 10;
int remainder = number / 10;
while (remainder > 0) {
// step 1
int currentUnitPosition = remainder % 10;
if (currentUnitPosition > previousUnitPosition) {
// step 2
decreasingNumber = true;
} else if (currentUnitPosition < previousUnitPosition) {
// step 3
increasingNumber = true;
}
// step 5
if (decreasingNumber && increasingNumber) {
return true;
}
// step 6
previousUnitPosition = currentUnitPosition;
remainder = remainder / 10;
}
return decreasingNumber && increasingNumber;
}
I'm pretty new to java, but I'm trying to make a simulation of the finger game, 'Sticks', using my limited knowledge. This may not be the neatest, but if you're going to make a suggestion on me to do something, link a page explaining what that thing is, and I'll read it.
Ok, so the issue comes up basically when I call a method to decide who's turn it is and trying to return the value for the "count" up to 5, but it's not returning to main()
public static int TurnCalcBB(int PLH, int PRH, int BRH, int BLH, int Death)
{
//Attacking with bot Right hand
Random botAtk = new Random();
if(botAtk.nextInt(2) == 1 && PRH <= 5)
{
PRH = BRH + PRH;
JOptionPane.showMessageDialog(null,"Your right hand is now at " + PRH);
return PRH;
} else if(botAtk.nextInt(2) == 0 && PLH <= 5){
PLH = BRH + PLH;
JOptionPane.showMessageDialog(null, "Your left hand is now at " + PLH);
return PLH;
}
return Death;
}
Death is there because I was getting an error telling me that I always need to return SOMETHING so I'm returning a static value.
Basically, the problem is getting PLH (player left hand) or PRH (player right hand) to return to main. If I'm not wrong, they should return as their initial variable name (PL, and PR) with the returned value correct? If not, what can I do to fix this?
The code is a lot larger than this, and this issue is happening throughout the whole program, so I'm showing just 1 method and assuming they're all the same issue; the methods are almost all the same.
Also, while I'm typing a question already, is nextInt() the best way to do a random number generator? When I had it as nextInt(1) it was exclusively attacking the left hand, and when I switched it to nextInt(2) now it's attacking both, but occasionally the code... "crashes" (what I mean by crashes is that it generates a number outside of what the If statements are looking for). I obviously need to to generate either a 1 or a 2 (or 0 and 1 if 0 counts).
You can change your code to
public static Integer TurnCalcBB(int PLH, int PRH, int BRH, int BLH, int Death)
{
//Attacking with bot Right hand
Random botAtk = new Random();
if(botAtk.nextInt(2) == 1 && PRH <= 5)
{
PRH = BRH + PRH;
JOptionPane.showMessageDialog(null,"Your right hand is now at " + PRH);
return PRH;
} else if(botAtk.nextInt(2) == 0 && PLH <= 5){
PLH = BRH + PLH;
JOptionPane.showMessageDialog(null, "Your left hand is now at " + PLH);
return PLH;
}
return null;
}
NOTE: make sure you first check for null values where you call this function.
You are generating random number twice, this is why you can observe "strange" behvior.
Random botAtk = new Random();
if(botAtk.nextInt(2) == 1 && PRH <= 5) {
...
}
else if(botAtk.nextInt(2) == 0 && PLH <= 5) {
...
}
Try generating random only once:
Random botAtk = new Random();
boolean right = botAtk.nextInt(2) == 1; // flip coin only once
if(right && PRH <= 5) {
...
}
else if(!right && PLH <= 5) {
...
}
I know the answer will not get accepted, because there is an accepted one, but nevertheless:
I suspect that you have a wrong understanding of method parameter passing in Java.
What I read from your question and comments is that you expect this to work:
public static int psInt = 0;
static void main() {
int someNumber = 1;
int someOtherNumber = 5;
method1( someNumber, someOtherNumber );
// You expect "someNumber" to be 6 right now.
// But in fact, the value will be unchanged.
// What WILL work: psInt is 0 now
method3(); // this method will modify the static class var
// psInt is 5 now.
}
static void method1( int numParam, int someothervalue ){
numParam = numParam + someothervalue;
}
static void method2( int someNumber, int someothervalue ){
someNumber = someNumber + someothervalue; // <- same name won't work either!
}
public static void method3(){
psInt = 5;
}
But in Java method arguments are passed by value. That is: a copy!
So no matter how you name the variables and arguments, you will never have an "out" argument here.
What you can do:
In a static method, you can use and modify static class variables.
In a non-static method, you can use and modify non-static and static class variables.
You can pass a State-Object, of which you can modify field values.
You can return a value.
... there are more possibilites. These just to start with.
In your case, 4. does not make so much sense, because you wouldn't know if it is the new right or left hand value.
I am currently learning the basics of Java from a book and I've got this code as an example of Nested Loops using Recursion. I understand everything, but the usage of return function in the end of the code. I cannot figure out how the program decide, when to stop exactly when K=4. I've tried to debug it and this continued to be like a mystery for me. Here is the code :
import java.util.Scanner;
public class nestedLoops {
public static int numberOfLoops;
public static int numberOfIterations;
public static int[] loops;
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("N = ");
numberOfLoops = input.nextInt();
System.out.print("K = ");
numberOfIterations = input.nextInt();
input.close();
loops = new int[numberOfLoops];
nestedLoops(0);
}
public static void nestedLoops(int currentLoop) {
if (currentLoop == numberOfLoops) {
printLoops();
return;
}
for (int counter=1;counter<=numberOfIterations;counter++) {
loops[currentLoop] = counter;
nestedLoops(currentLoop + 1);
}
}
public static void printLoops() {
for (int i = 0; i < numberOfLoops; i++) {
System.out.printf("%d ", loops[i]);
}
System.out.println();
}
}
It would be very helpful if someone explain me how return works in this particular example in the end when numbers are "4.4" and also how it works at all in a void method, because I've been searching for explanation of that but did not succeed...
Thank you beforehand !
A return statement in a void method stops running the method and returns back to the calling code. In this example with the input:
numberOfLoops = 4
numberOfIterations = 4
Right after taking the input, you create an array based off of the input and then call the nestedLoops(0) method:
public static void nestedLoops(int currentLoop) {
if (currentLoop == numberOfLoops) {
printLoops();
return;
}
for (int counter=1;counter<=numberOfIterations;counter++) {
loops[currentLoop] = counter;
nestedLoops(currentLoop + 1);
}
}
The explanation
For starts, let's just ignore the for loop. The if statement checks to see if currentLoop == numberOfLoops and it does this every time this method is called. Right now currentLoop is 0 (the value we passed into this method when we called it) and numberOfLoops is 4 (the value we entered at the very beginning) so this is false and none of the code inside is called.
The for loop below the if statement is going to run numberOfIterations times. In our case, this loop is going to run 4 times. I will write out what happens below in sequential order:
- input is 4, 4
- nestedLoops(0) called- currentLoop = 0
- if evaluates to false
- for loop runs
- loops[0] = 1
- nestedLoops(1)
- if evaluates to false ( 1 != 4)
- for loop runs
- loops[1] = 1
- nestedLoops(2)
- if evaluates to false (2 != 4)
- for loop runs
- loops[2] = 1
- nestedLoops(3)
- if evaluates to false (3 != 4)
- for loop runs
- loops[3] = 1
- nestedLoops(4)
- if evaluates to TRUE (4 == 4)
- loops are printed (all values are 1 right now)
-returns to calling location
-Which is the for loop associated with this indention.
-For loop increments, and then sets loops[3] = 2.
- then this loop finishes
- then this loop finishes
etc. etc.
The return in a void method just means "okay, stop what you're doing and go back to who/whatever called this and move on" In this case its jumping back to previous for loop to keep working.
The for loop inside the nestedLoops method is calling itself numberOfIterations times. So it goes 0, then makes numberOfIterations calls. So if you entered 4 you would see 4 calls with currentLoop=1 then 16 calls with currentLoop=2 and so on....
When all else fails write some code to debug your code. I am a visual person myself so making some output helps when the debugger doing it for me.
public static HashMap<Integer, Integer> map = new HashMap();
public static void main(String[] args) {
....
System.out.println(map);
}
public static void nestedLoops(int currentLoop) {
if(map.containsKey(currentLoop)) {
map.put(currentLoop, map.get(currentLoop)+1);
} else {
map.put(currentLoop, 1);
}
...
}