This is coding bat exercise: Java > Warmup-2 > stringX
What is the second block of code doing? Why does it produce the wrong answer?
public String stringX(String str) {
String answer = "";
for (int i = 0; i < str.length(); i++) {
if (str.substring(i , i+1).equals("x") && i != 0 && i != str.length()-1) {
answer = answer + "";
}
else {
answer = answer + str.substring(i , i + 1);
}
}
return answer;
}
vs
public String stringX(String str) {
String answer = "";
for (int i = 0; i < str.length(); i++) {
if (str.substring(i , i+1).equals("x") && i != 0 && i != str.length()-1) {
answer = answer + "";
}
answer = answer + str.substring(i , i + 1);
}
return answer;
}
The first block will run else only if the first if statement is false. else statement can only run if none of the above conditional statements returned true (if and else if). However the second block will run regardless of whether the first if statement true or false.
Check out this doc for further explanation: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/if.html
The 2nd block executes all the code shown and thus always takes the substring of answer
Related
I've been having trouble with this assignment:
Given a string, replace the first occurrence of 'a' with "x", the second occurrence of 'a' with "xx" and the third occurrence of 'a' with "xxx". After the third occurrence, begin the replacement pattern over again with "x", "xx", "xxx"...etc.; however, if an 'a' is followed by more than 2 other 'a' characters in a row, then do not replace any more 'a' characters after that 'a'.
No use of the replace method is allowed.
aTo123X("ababba") → "xbxxbbxxx"
aTo123X("anaceeacdabnanbag") → "xnxxceexxxcdxbnxxnbxxxg"
aTo123X("aabaaaavfaajaaj") → "xxxbxxxaaavfaajaaj"
aTo123X("pakaaajaaaamnbaa") → "pxkxxxxxxjxxaaamnbaa"
aTo123X("aaaak") → "xaaak"
My code's output is with a's included, x's added but not the correct amount of x's.
public String aTo123X(String str) {
/*
Strategy:
get string length of the code, and create a for loop in order to find each individual part of the String chars.check for a values in string and take in pos of the a.
if one of the characters is a
replace with 1 x, however, there aren't more than 2 a's immediately following first a and as it keeps searching through the index, add more x's to the original string, but set x value back to 1 when x reaches 3.
if one of characters isn't a,
leave as is and continue string.
*/
String xVal = "";
String x = "x";
String output = "";
for (int i = 0; i < str.length(); i++){
if( str.charAt(i) == 'a'){
output += x;
str.substring(i+1, str.length());
}
output += str.charAt(i);
}
return output;
}
This is the code that does the same. I've commented the code to explain what it does
public class ReplaceChar {
public static void main(String... args){
String[] input =new String[]{"ababba","anaceeacdabnanbag","aabaaaavfaajaaj"};
StringBuilder result = new StringBuilder();
for (int i= 0; i < input.length;i++){
result.append(getReplacedA(input[i]));
result.append("\n");
}
System.out.println(result);
}
private static String getReplacedA(String withA){
// stringBuilder for result
StringBuilder replacedString = new StringBuilder();
// counting the number of time char 'a' occurred in String for replacement before row of 'aaa'
int charACount = 0;
// get the first index at which more than two 'aa' occurred in a row
int firstIndexOfAAA = withA.indexOf("aaa") + 1;
// if 'aaa' not occurred no need to add the rest substring
boolean addSubRequired = false;
// if the index is 0 continue till end
if (firstIndexOfAAA == 0)
firstIndexOfAAA = withA.length();
else
addSubRequired = true;
char[] charString = withA.toCharArray();
//Replace character String[] array
String[] replace = new String[]{"x","xx","xxx"};
for(int i = 0; i < firstIndexOfAAA; i++){
if (charString[i] == 'a'){
charACount++;
charACount = charACount > 3 ? 1 : charACount ;
// add the number x based on charCount
replacedString.append(replace[charACount - 1]);
}else{
replacedString.append(charString[i]);
}
}
// if the String 'aaa' has been found previously add the remaining subString
// after that index
if (addSubRequired)
replacedString.append(withA.substring(firstIndexOfAAA));
// return the result
return replacedString.toString();
}
}
Output:
xbxxbbxxx
xnxxceexxxcdxbnxxnbxxxg
xxxbxxxaaavfaajaaj
EDIT : Some Improvement You can make for some corner cases in the getReplacedA() function:
Check if char 'a' is there or not in the String if not just return the String No need to do anything further.
Use IgnoreCase to avoid the uppercase or lowercase possibility.
Firstly, string is immutable, so the below statement does nothing
str.substring(i+1, str.length());
I guess you wanted to do:
str = str.substring(i+1, str.length());
However, even after fix that, your program still doesn't work. I can't really comprehend your solution. 1) you are not detecting more than 3 a's in a row. 2) you are not appending "xx" or "xxx" at all
Here is my version, works for me so far:
public static void main(String[] args) {
System.out.println(aTo123X("ababba")); // "xbxxbbxxx"
System.out.println(aTo123X("anaceeacdabnanbag")); // "xnxxceexxxcdxbnxxnbxxxg"
System.out.println(aTo123X("aabaaaavfaajaaj")); // "xxxbxxxaaavfaajaaj"
}
public static String aTo123X(String str) {
String output = "";
int aOccurrence = 0;
String[] xs = {"x", "xx", "xxx"};
for (int i = 0; i < str.length(); ++i) {
if (str.charAt(i) == 'a') {
output += xs[aOccurrence % 3]; // append the x's depending on the number of a's we have seen, modulus 3 so that it forms a cycle of 3
if (i < str.length() - 3 && str.charAt(i + 1) == 'a' && str.charAt(i + 2) == 'a' && str.charAt(i + 3) == 'a') {//if an 'a' is followed by more than 2 other 'a' characters in a row
output += str.substring(i + 1);
break;
} else {
++aOccurrence; // increment the a's we have encountered so far
}
} else {
output += str.charAt(i); // append the character if it is not a
}
}
return output;
}
public class NewClass {
public static void main(String[] args) {
System.out.println(aTo123X("ababba")); // "xbxxbbxxx"
System.out.println(aTo123X("anaceeacdabnanbag")); // "xnxxceexxxcdxbnxxnbxxxg"
System.out.println(aTo123X("aabaaaavfaajaaj")); //xxxbxxxaaavfaajaaj
}
public static String aTo123X(String str) {
String output = "";
int aCount = 0;
int inRow = 0;
for (int i = 0; i < str.length();) {
if (str.charAt(i) == 'a') {
if (inRow <= 1) {
inRow++;
aCount++;
if (aCount == 1) {
output += "x";
} else if (aCount == 2) {
output += "xx";
} else {
output += "xxx";
aCount = 0;
}
boolean multiple = ((i + 1) < str.length()) && (str.charAt(i + 1) == 'a')
&& ((i + 2) < str.length()) && (str.charAt(i + 2) == 'a');
if (multiple) {
i++;
while (i < str.length()) {
output += str.charAt(i++);
}
return output;
}
} else {
output += str.charAt(i);
}
} else {
output += str.charAt(i);
inRow = 0;
}
i++;
}
return output;
}
}
I am pointing out problems in your code in form of comments in the code itself.
public String aTo123X(String str) {
//You are not using xVal variable in your code, hence it's obsolete
String xVal = "";
//You don't need x variable as you can simply use string concatenation
String x = "x";
String output = "";
for (int i = 0; i < str.length(); i++) {
/**
* Here, in "if" block you have not implmented any logic to replace the 2nd and
* 3rd occurence of 'a' with 'xx' and 'xxx' respectively. Also, substring() returns
* the sub-string of a string but you are not accepting that string anywhere, and
* you need not even use sub-string as "for" loop will cycle through all the
* characters in the string. If use sub-string method you code will only process
* alternative characters.
*/
if( str.charAt(i) == 'a') {
output += x;
str.substring(i+1, str.length());
}
/**
* Because of this statement a's are also returned, because this statement gets
* in both scenarios, whether the current character of string is a or not.
* But, this statement should get executed only when current character of the
* string is 'a'. So, in terms of coding this statement gets executed no matter
* "if" loop is executed or not, but it should get executed only when "if" loop
* is not executed. So, place this statement in else block.
*/
output += str.charAt(i);
}
return output;
}
I have implemented the logic for you. Here is Solution for your problem, just copy and run it. It passes all the specified test cases.
public String aTo123X(String str) {
String output = "";
int count = 1;
boolean flag = true;
for (int i = 0; i < str.length(); i++) {
if(str.charAt(i) == 'a' && flag == true) {
switch(count) {
case 1: output += "x";
count++;
break;
case 2: output += "xx";
count++;
break;
case 3: output += "xxx";
count = 1;
break;
}
if ((str.charAt(i+1) == 'a' && str.charAt(i+2) == 'a') == true) {
flag = false;
}
}
else {
output += str.charAt(i);
}
}
return output;
}
I use Map To store where to replace
public static void main(String[] args) {
System.out.println(aTo123X("ababba"));//xbxxbbxxx
System.out.println(aTo123X("anaceeacdabnanbag"));//xnxxceexxxcdxbnxxnbxxxg
System.out.println(aTo123X("aabaaaavfaajaaj"));//xxxbxxxaaavfaajaaj
}
public static String aTo123X(String str){
String res = "";
int nthReplace = 1; //Integer to store the nth occurence to replace
//Map to store [key == position of 'a' to replace]
//[value == x or xx or xxx]
Map<Integer, String> toReplacePos = new HashMap<>();
//The loop to know which 'a' to replace
for (int i = 0; i < str.length(); i++) {
if(str.charAt(i) == 'a'){
toReplacePos.put(i, nthReplace % 3 == 1 ? "x": (nthReplace % 3 == 2 ? "xx": "xxx"));
nthReplace++;
//Break if an 'a' is followed by more than 2 other 'a'
try {
if((str.charAt(i+1) == 'a')
&& (str.charAt(i+2) == 'a')
&& (str.charAt(i+3) == 'a')){
break;
}
} catch (StringIndexOutOfBoundsException e) {
}
}
}
//Do the replace
for (int i = 0; i < str.length(); i++) {
res += toReplacePos.containsKey(i) ? toReplacePos.get(i) : str.charAt(i);
}
return res;
}
I have edited my answer. This one is giving the correct solution:
public static void main (String[] args) throws InterruptedException, IOException, JSONException {
System.out.println(aTo123X("ababba")); //xbxxbbxxx
System.out.println(aTo123X("anaceeacdabnanbag")); //xnxxceexxxcdxbnxxnbxxxg
System.out.println(aTo123X("aabaaaavfaajaaj")); //xxxbxxxaaavfaajaaj
}
public static String aTo123X(String str) {
String x = "x";
String xx = "xx";
String xxx = "xxx";
int a = 1;
int brek = 0;
String output = "";
for (int i = 0; i < str.length(); i++) {
if(str.charAt(i) == 'a' && a == 1) {
output += x;
str.substring(i+1, str.length());
a = 2;
try {
if(str.charAt(i+1) == 'a' && str.charAt(i+2) == 'a')
brek += 1;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
else if(str.charAt(i) == 'a' && a == 2) {
output += xx;
str.substring(i+1, str.length());
a = 3;
try {
if(str.charAt(i+1) == 'a' && str.charAt(i+2) == 'a')
brek += 1;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
else if(str.charAt(i) == 'a' && a == 3) {
output += xxx;
str.substring(i+1, str.length());
a = 1;
try {
if(str.charAt(i+1) == 'a' && str.charAt(i+2) == 'a')
brek += 1;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
else {
output += str.charAt(i);
brek = 0;
}
if(brek>0) {
output += str.substring(i+1);
break;
}
}
return output;
}
I'm currently working on the notReplace problem on codingbat. I've identified the section of code that is wrong but have not idea why. When notReplace("This is right") is called I get the output: "Thtest test right".
Why does the following section of the code run?
else if (!(Character.isLetter(i-1)) && i+2<len && !(Character.isLetter(i+2))){
newStr += "test";
i++;
}
When i==2, charAt(i-1)=='h' so the first condition is already not satisfied, since h is a letter but 'is' still gets replaced with 'test'. Any help appreciated. Full code below:
public String notReplace(String str) {
String newStr = "";
String iN = "is not";
int len = str.length();
for (int i=0; i<len; i++){
if (str.substring(i,Math.min(i+2,len)).equals("is")){
if (i==0 && i+2<len && !(Character.isLetter(i+2))){
newStr += iN;
i++;
}
else if (i+2==len && !(Character.isLetter(i-1))){
newStr += iN;
i++;
}
else if (!(Character.isLetter(i-1)) && i+2<len && !(Character.isLetter(i+2))){
newStr += "test";
i++;
}
else newStr += str.charAt(i);
}
else newStr += str.charAt(i);
}
return newStr;
}
Character.isLetter(i - 1)
when i =2
Character.isLetter(i-1) --> Character.isLetter(1)
so it's false and because 1 is not a letter . your first condition !Character.isLetter(i - 1) is true.you have missed charAt(i-1) part
you should use
!Character.isLetter(charAt(i-1))
All i need this method to do is take a string lets say "aaxbb" and it will return true because there is an 'aa' and a 'bb',
If the string given is length = 0 or length = 1 it should fail.
The issue i'm having is that which i do not know.. i know that in my terminal after hasAdjacentPair's first test case Pass's, i get a blinking curser meaning that somehwere in this method i'm not kicking out of one of my loops for it to continue to check the string for any more adjacent pairs
the first test case passes while its an empty string "" = because it returned false
the second test case passes while its "a" = because it returned false
We are also not allowed to use Arrays :(
public boolean hasAdjacentPair(String str)
{
boolean result = false;
if (str.length() == 0)
{
result = false;
}
if (str.length() == 1)
{
result = false;
}
while (str.length() != 0)
{
for (int i = 0; i < str.length() - 1; ++i)
{
char adjChar = str.charAt(i);
char nextAdjChar = str.charAt(i + 1);
if (adjChar == nextAdjChar)
{
result = true;
}
}
}
return result;
}
Changed my while loop while (str.length() != 0) to while (str.length() != 0 && str.length() != 1) this enabled test 2 to work
EDIT 2 : After i completely took out the while (str.length() != 0) All 5 of my test cases pass :) so i guess it was just that?
while (str.length() != 0)
is always true and loop never end. Instead of if..if..while structure use either switch on length of string or if-else.
You could try something like this
if (str.length() == 0)
{
result = false;
}
else if (str.length() == 1)
{
result = false;
}
else
{
for (int i = 0; i < str.length() - 1; ++i)
{
char adjChar = str.charAt(i);
char nextAdjChar = str.charAt(i + 1);
if (adjChar == nextAdjChar)
{
result = true;
break;
}
}
If you checking for atleast one pair make use of break statement as you already know that you got the result
try this alternative:
boolean c = false;
//Your other code
while (str.length() != 0 && c == false)
{
for (int i = 0; i < str.length() - 1; ++i)
{
char adjChar = str.charAt(i);
char nextAdjChar = str.charAt(i + 1);
if (adjChar == nextAdjChar)
{
result = true;
}
}
c = true;
}
//Your other code
Is there a reason you have a while loop checking for the str length? The str is not modified in the loop.
What you most likely want is an if, else if, else structure.
You can most likely return true within the adjChar == nextAdjChar if statement and return false at the end of your function.
I am coding a simple chatbot, and my method seems to be stuck in a loop.
This below is the method, and I suspect there is a problem with the while loop, but I cannot find where I am messing up. No problems with compiling and running other than the stuck loop.
The loop below takes in a complete string, statement, loops for specific keywords, goal, and the starts looking through the string at startPos
private int findKeyword(String statement, String goal, int startPos)
{
String phrase = statement.trim();
int psn = phrase.toLowerCase().indexOf(goal.toLowerCase(), startPos);
while (psn >= 0)
{
String before = " ", after = " ";
if (psn > 0)
{
before = phrase.substring(psn-1, psn).toLowerCase();
}
if (psn + goal.length() < phrase.length())
{
after = phrase.substring(psn + goal.length(), psn + goal.length() + 1).toLowerCase();
}
if (((before.compareTo("a") < 0) || (before.compareTo("z") > 0)) && ((after.compareTo("a") < 0) || after.compareTo("z") > 0))
{
return psn;
}
psn = phrase.indexOf(goal.toLowerCase(), psn + 1);
}
return -1;
}
psn = phrase.indexOf(goal.toLowerCase(), psn + 1);
will never rich to (psn < 0) thats the problem
Here is the problem: Return true if the string "cat" and "dog" appear the same number of times in the given string. Examples: catDog("catdog") → true; catDog("catcat") → false; catDog("1cat1cadodog") → true
public boolean catDog(String str) {
int countCat=0;
int countDog=0;
for (int i=0; i<str.length();i++)
{
if (str.charAt(i)== 'c'&& str.length()>=3)
{
if (str.substring(i,i+3).equals("cat"))
countCat++;
}
}
for (int i=0; i<str.length();i++)
{
if (str.charAt(i)== 'd' && str.length()>=3)
{
if (str.substring(i,i+3).equals("dog"))
countDog++;
}
}
if (countCat == countDog)
return true;
else
return false;
}
In your for loops conditions you are checking if entire String has length greater or equal 3 instead of checking only part from i till end. Try maybe with
str.length() - i >= 3
instead of
str.length() >= 3
str.substring(i,i+3).equals("cat")
i might be the last and i+3 will give an error
Why don't you simply use StringUtils#countMatches?
StringUtils.countMatches(myStr, "cat") == StringUtils.countMatches(myStr, "dog");
Don't get lost with the indexes. However, if you don't want to use this method, debugging your code is the best thing you can do.
Okay, this is what I might do:
The problem was with your check str.length() >= 3. It should have been i + str.length().
I also suggest some changes to your code to get rid of duplication. Here I extracted the part that counts the number of appearances of a substring and moved it to its own method. The part that checks if count of cat equals count of dog now calls said method twice.
public static void main(String[] args) {
System.out.println(catDog("catdog"));
System.out.println(catDog("catcat"));
System.out.println(catDog("1cat1cadodog"));
System.out.println(catDog("catdogcatc"));//Would previously throw error.
}
public static boolean catDog(String str) {
int countCat = countAppearances(str, "cat");
int countDog = countAppearances(str, "dog");
return countCat == countDog;
}
private static int countAppearances(String str, String key) {
int count = 0;
for (int i = 0; i < str.length(); i++) {
if (str.charAt(i) == key.charAt(0) && i + key.length() <= str.length()) {
if (str.substring(i, i + key.length()).equals(key)) {
count++;
}
}
}
return count;
}
You need to update your first condition before spiting you string like:
if (str.charAt(i)== 'c' && (str.length() - i) >= 3)
{
if (str.substring(i,i+3).equals("cat"))
countCat++;
}
public boolean catDog(String str) {
int catCount = 0, dogCount = 0;
//run a for loop to check cat count
//run loop till 2nd last character
for (int i = 0; i < str.length() - 2; i++) {
//now check if the charaters at positions matches "cat"
//if matches then increment cat count
if (str.charAt(i) == 'c' && str.charAt(i + 1) == 'a' && str.charAt(i + 2) == 't') {
catCount++;
} else if (str.charAt(i) == 'd' && str.charAt(i + 1) == 'o' && str.charAt(i + 2) == 'g') {
//else check if the charaters at positions matches "dog"
//if matches then increment dog count
dogCount++;
}
}
//check cat count and dog count
if (catCount == dogCount) {
return true;
} else {
return false;
}
}