Currently I have a simple problem to solve:
Given a String str, what is the best way of counting the amount of alphabetic literals in the string?
Right now I am thinking something like this:
int letterCount = 0;
for(int i = 0 : str){
String check = "" + str.charAt(i);
if(check.isLetter())
letterCount++
}
Are there any more efficient or elegant ways?
I’m pretty fond of streams (since Java 8):
String str = "A string";
long letterCount = str.chars().filter(Character::isLetter).count();
System.out.println(letterCount);
7
Your for loop is another nice solution. Here’s a version that works:
for (int index = 0; index < str.length(); index++) {
if (Character.isLetter(str.charAt(index))) {
letterCount++;
}
}
String str = "#CodeWines65";
int upper = 0, lower = 0, number = 0, special = 0;
for(int i = 0; i < str.length(); i++)
{
char ch = str.charAt(i);
if (ch >= 'A' && ch <= 'Z')
upper++;
else if (ch >= 'a' && ch <= 'z')
lower++;
else if (ch >= '0' && ch <= '9')
number++;
else
special++;
}
System.out.println("Lower case letters : " + lower);
System.out.println("Upper case letters : " + upper);
System.out.println("Number : " + number);
System.out.println("Special characters : " + special);
// If you are not concerned about uppercase or lowercase you can add them both & get the total count
This question already has answers here:
What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?
(26 answers)
Closed 4 years ago.
I have been trying to find my own way of making a Rot13 algorithm in java, but when I try a phrase, it gives me this error:
java.lang.ArrayIndexOutOfBoundsException: 41
So this is my code:
:Update with whole names,
public class Rot13
{
char[] translated;
String abc = "abcdefghijklmnopjrstuvwxyzabcdefghijklmnopqrstuvwxyz";
public String ROT13(String input){
input = input.toLowerCase();
char[] sentence = input.toCharArray();
char[] ABC = abc.toCharArray();
int x = input.length();
int y = 0;
char[] translated = new char[x];
for(int i = 0; i<x;i++){
int z = 0;
if(sentence[i] == ' '){
translated[i] = ' ';
}
else {
while(y==0){
if (sentence[i] == ABC[z]){
y =1;
}
else{
z += 1;
}
}
translated[i] = ABC[z+12];
}
}
String rot13string = new String(translated);
return rot13string;
}
}
: Update 2
I just tested this version again and it translates the it. But in the wrong way, for example, "Hello" becomes "tmmmm" The first letter seems to be right but then the next ones are always 'm'.
Update 3: Thanks for your answers guys, here is my final code, I just duplicated my alphabet a "few" times. :
public class ROT13
{
char[] translated;
String ab = "abcdefghijklmnopjrstuvwxyzabcdefghijklmnopqrstuvwxyz";
String abc = String.format("%0" + 1000 + "d", 0).replace("0",ab);
public String ROT13(String input){
input = input.toLowerCase();
char[] sentence = input.toCharArray();
char[] ABC = abc.toCharArray();
int length = input.length();
char[] translated = new char[length];
for(int i = 0; i<length;i++){
int y = 0;
int h = 0;
if(sentence[i] == ' '){
translated[i] = ' ';
}
else {
while(y==0){
int z = 0;
if (sentence[i] == ABC[h]){
y +=1;
}
else{
z += 1;
h += 1;
}
}
translated[i] = ABC[h+13];
}
}
String rot13string = new String(translated);
return rot13string;
}
}
Currently, think about what happens when there is a 'z' in the sentence. Then, you make t[i] = ABC[z (26) + 12] //which is larger than ABC's length.
Personally, I would do rot13 like so:
public char rot13(char s){
if (c >= 'a' && c <= 'm') return c += 13;
else if (c >= 'A' && c <= 'M') return c += 13;
else if (c >= 'n' && c <= 'z') return c -= 13;
else if (c >= 'N' && c <= 'Z') return c -= 13;
else return c;
}
Given is the following String:
String s = "Qba'g sbetrg gb qevax lbhe Binygvar";
My desired output is:
Don't forget to drink your ovaltine
My code:
public static String decrpyt(String s){
String ans = "";
for (int i = 0; i<s.length(); i++) {
int x = s.charAt(i);
if (x <= 105) {
char c = ((char) (x + 13));
ans += c;
} else {
char c = ((char) (x - 13));
ans += c;
}
}
return ans;
}
It returns:
don4t-forget-to-drink-_our-ovaltine
What do I need to do to get the desired output?
You are changing all characters, not just the letters, as has been mentioned in a comment. Carefully consider the range of characters that are letters that you need to modify. Declare x to be a char so that you don't have to consider the actual numeric ranges.
A-M => N-Z Action: += 13
a-m => n-z Action: += 13
N-Z => A-M Action: -= 13
n-z => a-m Action: -= 13
(all others) Action: No change
This can be expressed in 3 cases:
if ((x >= 'a' && x <= 'm') || (x >= 'A' && x <= 'M')) {
// Add 13
} else if ((x >= 'n' && x <= 'z') || (x >= 'N' && x <= 'Z')){
// Subtract 13
} else {
// Use as is
}
You can add in an idea of exception characters. Basically any character in the exception list won't be translated. This would look something like:
public static String decrpyt(String s){
String ans = "";
for(int i = 0; i<s.length(); i++){
// Could use a list or whatever, just giving you the idea here
String characterAt = s.charAt(i).toString();
if(characterAt.equals("'") || characterAt.equals(" "))
{
continue;
}
int x = s.charAt(i);
if(x <= 105) {
char c = ((char) (x + 13));
ans += c;
}
else{
char c = ((char) (x - 13));
ans += c;
}
}
return ans;
}
(EDITED)
My problem statement: write a method that will encode the String passed to the method by adding 13 letters to each character in the String. If the letter after adding 13 exceeds 'z' then "wrap around" the alphabet. Then return the encoded String.
encodeString("hello") → "uryyb"
encodeString("pie") → "cvr"
encodeString("book") → "obbx"
this is what I have so far :
public static String encodeString (String input) {
String output;
for (int i = 0; i < input.length(); i++) {
char c = input.charAt(i);
if (c >= 'a' && c <= 'm')
c += 13;
else if (c >= 'n' && c <= 'z')
c -= 13;
output= (" " + (c));
}
return output;
}
now I know that I have to create a counter so that the method will continue to loop until it reaches the length of the string passed...and I know that if the charAt(index) is less than the character 'n' that I add 13 and if it is greater then I subtract 13. when I put it all together though I just get so confused and just get a bunch of compiling errors like Type mismatch: cannot convert from int to String.
note straightforward explanations/answers would be much appreciated...
***so now my problem is that it keeps telling me my output variable may not have been initialized
This code is not the most performatic but works good with Upper and Lower characters.
hElLo → uRyYb
pIe → cVr
bOoK → oBbX
private static String encodeString(String string) {
char[] ret = new char[string.length()];
for (int i = 0; i < string.length(); i++) {
ret[i] = rot13(string.charAt(i));
}
return String.valueOf(ret);
}
public static char rot13(char c) {
if (Character.isLetter(c)) {
if (Character.compare(Character.toLowerCase(c), 'a') >= 0
&& Character.compare(Character.toLowerCase(c), 'm') <= 0)
return c += 13;
else
return c -= 13;
}
return c;
}
You have to initialize your output variable as an empty String. Furthermore you are always replacing the contents of the output variable with the last char you've just encoded. So you have to add every char to the output with += instead of =.
So here is the fixed solution:
public static String encodeString(String input) {
String output = ""; // initialize as empty String
for (int i = 0; i < input.length(); i++) {
char c = input.charAt(i);
if (c >= 'a' && c <= 'm') {
c += 13;
} else if (c >= 'n' && c <= 'z') {
c -= 13;
}
output += " " + c; // add all chars to the String instead of replacing the whole String with "="!
}
return output;
}
I beautified your code a bit, so everybody can see what it really does.
Use an IDE!
Given a polynomial with a single variable x, and the value of x as input, compute its value. Examples:
eval("-2x^3+10x-4x^2","3")=-60
eval("x^3+x^2+x","6")=258
Description of issue: In this code I break the string into a substring whenever a +/- is encountered and pass the substring to a function which evaluates single term like "-2x^3". So my code for input = "-2x^3+10x-4x^2" calculates till "-2x^3+10x" only and skips "-4x^2" part.
Can anyone please tell me whats wrong here?
public class EvalPolyX2 {
static String testcase1 = "-2x^3+10x-4x^2";
static String testcase2 = "3";
public static void main(String args[]){
EvalPolyX2 testInstance = new EvalPolyX2();
int result = testInstance.eval(testcase1,testcase2);
System.out.println("Result : "+result);
}
public int eval(String str,String valx){
int sum = 0;
String subStr = "";
if(str.charAt(0) == '-')
{
int len = str.length();
for (int i = 0; i < len; i++)
{
if(str.charAt(i) == '-' || str.charAt(i) == '+')
{
subStr = str.substring(0, i);
System.out.println("subStr="+subStr);
sum += evalSubPoly(subStr, valx);
str = str.substring(i);
len = str.length();
i = 0;
}
}
}
else if(str.charAt(0) != '-')
{
str = '+' + str;
int len = str.length();
for (int i = 0; i < len; i++)
{
if(str.charAt(i) == '-' || str.charAt(i) == '+')
{
subStr = str.substring(0, i);
System.out.println("subStr="+subStr);
sum += evalSubPoly(subStr, valx);
str = str.substring(i);
len = str.length();
i=0;
}
}
}
return sum;
}
public int evalSubPoly(String poly,String valx){
int len = poly.length();
String num = "";
String power = "";
int exp = 0, coeff = 0;
for(int i = 0; i < len; i++)
{
if(poly.charAt(i) == 'x')
{
num = poly.substring(0, i);
coeff = Integer.parseInt(num);
}
if(poly.charAt(i) == '^')
{
power = poly.substring(i+1, len);
exp = Integer.parseInt(power);
}
}
if(power.equals(""))
exp = 1;
System.out.println("coeff="+coeff);
int sum = 1;
int x = Integer.parseInt(valx);
for (int i = 0; i < exp; i++)
{
sum = sum*x;
}
System.out.println("sum="+sum);
sum = sum*coeff;
return sum;
}
}
What's wrong with using regex? You can split the polynomial into monomials, evaluate each, and add all of the results.
private static final Pattern monomial = Pattern
.compile("([+-])?(\\d+)?x(?:\\^(\\d+))?");
public static int eval(String str, String valx) {
Matcher m = monomial.matcher(str);
int x = Integer.parseInt(valx);
int total = 0;
while (m.find()) {
String mul = m.group(2);
int value = (mul == null) ? 1 : Integer.parseInt(m.group(2));
String pow = m.group(3);
value *= (pow == null) ? x : (int) Math.pow(x,
Integer.parseInt(pow));
if ("-".equals(m.group(1)))
value = -value;
total += value;
}
return total;
}
System.out.println(eval("-2x^3+10x-4x^2", "3"));
System.out.println(eval("x^3+x^2+x", "6"));
-60
258
This code replacement should help
if(str.charAt(i) == '-' || str.charAt(i) == '+' || i == (len - 1))
{
if(i == len - 1)
{
i++;
}
...
Though there could be better ways, but I only wanted to show a way out here.
The reason is you are looking for + or - as the delimiter.
But the last part of the expression will not end with either of these but just probably EOL
You need to account for the last term (the if-statement will only trigger when a - or + is found, which there isn't at the end).
One easy way to do this is to replace:
for (int i = 0; i < len; i++)
{
if (str.charAt(i) == '-' || str.charAt(i) == '+')
with:
// v one more iteration
for (int i = 0; i <= len; i++)
{
if (i == len || str.charAt(i) == '-' || str.charAt(i) == '+')
// \------/
// extra condition
The above simply goes on for one more iteration and, on that iteration, always goes into the if-statement, causing the last term to be processed.
You can also simplify
if (str.charAt(0) == '-')
{
// common code
}
else if (str.charAt(0) != '-')
{
str = '+' + str;
// common code
}
To:
if (str.charAt(0) != '-')
{
str = '+' + str;
}
// common code
There's also a bug with handling +. I get a NumberFormatException for this. One way to handle it is to ignore the + between the terms (and not adding a + to the start):
if (i != len && str.charAt(i) == '+')
str = str.substring(i+1);
else
str = str.substring(i);
And you might as well make your functions static and call them directly rather than declaring a new instance of your class.
Test.
The simple answer is that when you do this:
if(str.charAt(i) == '-' || str.charAt(i) == '+')
{
subStr = str.substring(0, i);
the effect is that you're setting subStr to text just before the - or +, and evaluating it. But since there's no - or + at the end of the string, there's no way this logic will evaluate the last term of the polynomial, since it only evaluates substrings that are right before a - or +.
P.S. That's just one problem I noticed. I don't know if the rest of the logic is correct.
When you parse the string, you look for +/- and only stop if you find them. This works for the first two terms, but when you get down to "-4x^2" the loop won't stop because there is no +/-. So in addition to the conditions you have, you need to add code so that when the end of the string is reached, what you have left is the last term. So what you want to have is this
if(str.charAt(0) == '-')
{
int len = str.length();
for (int i = 0; i < len; i++)
{
if(str.charAt(i) == '-' || str.charAt(i) == '+')
{
subStr = str.substring(0, i);
System.out.println("subStr="+subStr);
sum += evalSubPoly(subStr, valx);
str = str.substring(i+1);
len = str.length();
i = 0;
}
}
System.out.println("subStr="+str);
sum += evalSubPoly(str, valx);
}
else if(str.charAt(0) != '-')
{
str = '+' + str;
int len = str.length();
for (int i = 0; i < len; i++)
{
if(str.charAt(i) == '-' || str.charAt(i) == '+')
{
subStr = str.substring(0, i);
System.out.println("subStr="+subStr);
sum += evalSubPoly(subStr, valx);
str = str.substring(i+1);
len = str.length();
i=0;
}
}
System.out.println("subStr="+str);
sum += evalSubPoly(str, valx);
}
I will also throw out the disclaimer that there may be more errors, but this is the major one causing your problem.
EDIT: added change to else if statement and added change mentioned in my comment above
With regular expressions, you can get a more simple solution. And, do you want support for simple constants? Try the next:
public class EvalPolyX2 {
public static void main(String args[]) {
System.out.println("Result: " + eval("x^3+x^2+x", 6));
}
public static int eval(String eq, int val) {
int result = 0;
String mons[] = eq.split("(?=[+-])(?!\\B)");
for (String str : mons) {
str = str.replace("+", "");
if (str.contains("x")) {
double a = 1, b = 1;
String[] comps = str.split("x\\^?");
if (comps.length > 0) {
a = comps[0].isEmpty() ? 1 : Integer.parseInt(comps[0]);
}
if (comps.length > 1) {
b = Integer.parseInt(comps[1]);
}
result += a * Math.pow(val, b);
} else {
result += Integer.parseInt(str);
}
}
return result;
}
}