class Solution {
public String reverseWords(String s) {
int count = 0;
int current = 0;
StringBuilder build = new StringBuilder();
for(int i = 0; i< s.length(); i++){
count++;
current = count;
if(s.charAt(i) == ' '){
while(current > 0){
build.append(s.charAt(current - 1));
current--;
}
build.append(s.charAt(i));
}
}
return build.toString();
}
}
I am having trouble understanding why this doesn't work. I went through the
entire code a couple of times but there seems to be an issue.
Input : "Let's take LeetCode contest"
my answer: " s'teL ekat s'teL edoCteeL ekat s'teL "
correct answer: "s'teL ekat edoCteeL tsetnoc"
whats going on?
There are several problems:
You set current to the current position, and then iterate down to 0 append characters. Instead of going down to 0, you iterate until the beginning of the last word. Alternative, iterate until the previous ' ' character.
You only append something after seeing a ' ' character. What will happen at the end of the sentences? As i goes over the letters in the last word, there will be no more ' ' characters, and so the last word will never get appended. To handle this case, you would need to add some logic after the for-loop to check if there is an unwritten word, and append it reversed.
A simpler approach is to take advantage of the StringBuilder's ability to insert characters at some position.
You could track the beginning position of the current word,
and as you iterate over the characters,
insert if it's not ' ',
or else append a ' ' and reset the insertion position.
StringBuilder build = new StringBuilder();
int current = 0;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (c == ' ') {
build.append(' ');
current = i + 1;
} else {
build.insert(current, c);
}
}
return build.toString();
Use a StringBuilder to reverse each word in your String :
String input = "Let's take LeetCode contest";
String[] split = input.split(" +");
StringBuilder output = new StringBuilder();
for (int i = 0; i < split.length; i++) {
output.append(new StringBuilder(split[i]).reverse());
if(i<input.length()-1)
output.append(" ");
}
System.out.println(output);
First, you skip over index 0. Put these lines at the end of your method to avoid this:
count++;
current = count;
You might need a variable to track where the current word began. For example, declare one along with count and current like this:
int wordStart = 0;
Then, when you finish processing a word, set wordStart to point to the first character of the next word. I would put that after the while loop, here:
build.append(s.charAt(i));
wordStart = count + 1;
You will also need to change this: while(current > 0){ to this: while(current >= wordStart)
Also: you don't need count. The variable i is the exact same thing.
You can use stream-api for your goal:
Stream.of(str.split(" "))
.map(s -> new StringBuilder(s).reverse().toString())
.reduce((s1, s2) -> s1 + " " + s2)
.orElse(null);
This is the easy way:
return Arrays.stream(s.split(" " ))
.map(StringBuilder::new)
.map(StringBuilder::reverse)
.map(StringBuilder::toString)
.collect(Collectors.joining(" "));
Related
everyone. I have a task- reverse every word in a sentence as long as the word is 5 or more letters long. The program has been working with most words, but after a couple, the words are not included. Does anyone know why this is happening? Here is the code:
public static int wordCount(String str) {
int count = 0;
for(int i = 0; i < str.length(); i++) if(str.charAt(i) == ' ') count++;
return count + 1;
}
This just gets the word count for me, which I use in a for loop later to loop through all the words.
public static String reverseString(String s) {
Stack<Character> stack = new Stack<>();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < s.length(); i++) {
stack.push(s.charAt(i));
}
while (!stack.empty()) {
sb.append(stack.pop());
}
return sb.toString();
}
This reverses a single string. This is not where I reverse certain words- this reverses a string. "Borrowed" from https://stackoverflow.com/a/33458528/16818831.
Lastly, the actual function:
public static String spinWords(String sentence) {
String ans = "";
for(int i = 0; i <= wordCount(sentence); i++) {
if(sentence.substring(0, sentence.indexOf(' ')).length() >= 5) {
ans += reverseString(sentence.substring(0, sentence.indexOf(' '))) + " ";
sentence = sentence.substring(sentence.indexOf(' ') + 1);
} else {
ans += sentence.substring(0, sentence.indexOf(' ')) + " ";
sentence = sentence.substring(sentence.indexOf(' ') + 1);
}
}
return ans;
}
This is where my mistake probably is. I'd like to know why some words are omitted. Just in case, here is my main method:
public static void main(String[] args) {
System.out.println(spinWords("Why, hello there!"));
System.out.println(spinWords("The weather is mighty fine today!"));
}
Let me know why this happens. Thank you!
The main issue would appear to be the for loop condition in spinWords()
The word count of your sentence keeps getting shorter while at the same time, i increases.
For example:
i is 0 when the word count is 5
i is 1 when the word count is 4
i is 2 when the word count is 3
i is 3 when the word count is 2 which
stops the loop.
It can't get through the whole sentence.
As many have mentioned, using the split method would help greatly, for example:
public static String spinWords(String sentence) {
return Arrays.asList(sentence.split(" ")).stream()
.map(word -> word.length() < 5 ? word : new StringBuilder(word).reverse().toString())
.collect(Collectors.joining(" "));
}
I think you should rewrite a lot of your code using String.split(). Instead of manually parsing every letter, you can get an array of every word just by writing String[] arr = sentence.split(" "). You can then use a for loop to go through and reverse each word something like this
for (int i=0; i<arr.length; i++) {
if (arr[i] >= 5) {
arr[i] = reverse(arr[i])
}
}
I know you just asked for a solution to your current code, but this would probably get you a better grade :)
I am trying to answer this question.
Move the first letter of each word to the end of it, then add "ay" to the end of the word. Leave punctuation marks untouched.
This is what I did so far:
public static String pigIt(String str) {
//Populating the String argument into the String Array after splitting them by spaces
String[] strArray = str.split(" ");
System.out.println("\nPrinting strArray: " + Arrays.toString(strArray));
String toReturn = "";
for (int i = 0; i < strArray.length; i++) {
String word = strArray[i];
for (int j = 1; j < word.length(); j++) {
toReturn += Character.toString(word.charAt(j));
}
//Outside of inner for loop
if (!(word.contains("',.!?:;")) && (i != strArray.length - 1)) {
toReturn += Character.toString(word.charAt(0)) + "ay" + " ";
} else if (word.contains("',.!?:;")) {
toReturn += Character.toString(word.charAt(0)) + "ay" + " " + strArray[strArray.length - 1];
}
}
return toReturn;
}
It is supposed to return the punctuation mark without adding "ay" + "". I think I am overthinking but please help. Please see the below debugger.
One of the problems here is that your else if statement is never being invoked. The .contains method will not work with multiple characters like that unless you are trying to match them all. In your conditions you are essentially asking if the word matches that entire string "',.!?:;". If you just keep the exclamation point in there it will work invoke it. I don't know how else you can use contains besides making a condition for each one like word.contains("!")|| word.contains(",")|| word.contains("'"), etc.. You can also use regex for this problem.
Alternatively, you can use something like,
Character ch = new Character(yourString.charAt(i));
if(!Character.isAlphabetic(yourString.charAt(i))) {
to determine if a character is not an alphabetical one, and is a symbol or punctuation.
I think the best way is not relay on str.split("\\s++"), because you could have punctuation in any plase. The best one is to look through the string and find all not letter or digit symbols. After that you can define a word borders and translate it.
public static String pigIt(String str) {
StringBuilder buf = new StringBuilder();
for (int i = 0, j = 0; j <= str.length(); j++) {
char ch = j < str.length() ? str.charAt(j) : '\0';
if (Character.isLetterOrDigit(ch))
continue;
if (i < j) {
buf.append(str.substring(i + 1, j));
buf.append(str.charAt(i));
buf.append("ay");
}
if (ch != '\0')
buf.append(ch);
i = j + 1;
}
return buf.toString();
}
Output:
System.out.println(pigIt(",Hello, !World")); // ,elloHay, !orldWay
Regex may be difficult to start with but is very powerful:
public static String pigIt(String str) {
return str.replaceAll("([a-zA-Z])([a-zA-Z]*)", "$2$1ay");
}
The () specify groups. So I have one group with the first alphabet character and a second group with the remaining alphabet characters.
In the replace parameter you can refer to these groups ($1, $2).
String.replaceAll will search all matching string parts and apply the replacement. Non matching characters like the punctuations are left untouched.
public static void main(String[] args) {
System.out.println("Hello, World, ! -->"+ pigIt("Hello, World, !"));
System.out.println("Hello?, Wo$, F, ! -->"+ pigIt("Hello?, Wo$, F, !"));
}
The output of this method is:
Hello, World, ! -->elloHay, orldWay, !
Hello?, Wo$, F, ! -->elloHay?, oWay$, Fay, !
Im trying to reverse characters in a sentence without using the split function. Im really close but I am missing the final letter. Can some one please point me in the right direction? Right now it prints "This is a new sentence" as "sihT si a wen cnetnes" Also I included if(start == 0) because the program would skip the initial space character, but I don't understand why?
static String reverseLetters(String sentence)
StringBuilder reversed = new StringBuilder("");
int counter = 0;
int start = 0;
String word;
for(int i = 0; i <= sentence.length()-1 ; i++ )
{
if(sentence.charAt(i)== ' '|| i == sentence.length()-1 )
{
StringBuilder sb = new StringBuilder("");
sb.append(sentence.substring(start,i));
if(start == 0)
{
start = i;
word = sb.toString();
reversed.append(reverseChar(word));
reversed.append(' ');
}
else
{
start = i;
word = sb.toString();
reversed.append(reverseChar(word));
}
}
return reversed.toString();
}
static String reverseChar (String word)
{
StringBuilder b = new StringBuilder("");
for(int idx = word.length()-1; idx >= 0; idx -- )
{
b.append(word.charAt(idx));
}
return b.toString();
}
start means wordStart. As i points to the space, the next wordStart should point after i.
Hence the last i should point after the last word char, should be length()
the if-then-else is too broad; a space has to be added in one case: i pointing at the space.
One could loop unconditionally, and on i == length() break in the middle of the loop code.
I think the error lies in the index, the for should be
for(int i = 0; i <= sentence.length() ; i++ )
Then if should be:
if (sentence.charAt(i==0?0:i-1)== ' '|| i == sentence.length() )
For me the error will be that the substring(start,i) for the last one i should be sentence.length instead of sentence.length-1, so this would solve it.
Substring is open in the last index, so if you put substring(1, 10) will be substring from 1 to 9. That might be the problem with last word.
The thing with the first space is also the problem with substring, let's say you're reading "this is..." the first time it will do a subtring with start=0 and i = 4 so you expect "this " but it really is "this". The next reading, with start=4 and i=7 will be " is".
So with the change of the index you should be able to remove the if/else with start==0 too.
Another option
private String reverse (String originalString) {
StringBuilder reverseString = new StringBuilder();
for (int i = originalString.length() - 1; i >= 0; i--) {
reverseString.append(originalString.charAt(i));
}
return reverseString.toString();
}
String reverseString = "This is a new sentence";
System.out.println(new StringBuffer(reverseString).reverse().toString());
Syso prints : ecnetnes wen a si sihT
Put
i <= sentence.length()
In your for loop and change the if to:
if(i == sentence.length() || sentence.charAt(i)== ' ')
as
substring(start,i)
Returns the string up to i, not included.
import java.util.Stack;
public class Class {
public static void main(String[] args) {
String input = "This is a sentence";
char[] charinput = input.toCharArray();
Stack<String> stack = new Stack<String>();
for (int i = input.length() - 1; i >= 0; i--) {
stack.push(String.valueOf(charinput[i]));
}
StringBuilder StackPush = new StringBuilder();
for (int i = 0; i < stack.size(); i++) {
StackPush.append(stack.get(i));
}
System.out.println(StackPush.toString());
}
}
Not a split to be seen.
Consider the following inputs:
String[] input = {"a9", "aa9", "a9a9", "99a99a"};
What would be the most efficient way whilst using a StringBuilder to replace any digit directly prior to a nine with the next letter after it in the alphabet?
After processing these inputs the output should be:
String[] output = {"b9", "ab9", "b9b9", "99b99a"}
I've been scratching my head for a while and the StringBuilder.setCharAt was the best method I could think of.
Any advice or suggestions would be appreciated.
Since you have to look at every character, you'll never perform better than linear in the size of the buffer. So you can just do something like
for (int i=1; buffer.length() ++i) // Note this starts at "1"
if (buffer.charAt[i] == '9')
buffer.setCharAt(i-1, buffer.getCharAt(i-1) + 1);
You can following code:
String[] input = {"a9", "aa9", "a9a9", "99a99a", "z9", "aZ9"};
String[] output = new String[input.length];
Pattern pt = Pattern.compile("([a-z])(?=9)", Pattern.CASE_INSENSITIVE);
for (int i=0; i<input.length; i++) {
Matcher mt = pt.matcher(input[i]);
StringBuffer sb = new StringBuffer();
while (mt.find()) {
char ch = mt.group(1).charAt(0);
if (ch == 'z') ch = 'a';
else if (ch == 'Z') ch = 'A';
else ch++;
mt.appendReplacement(sb, String.valueOf(ch));
}
mt.appendTail(sb);
output[i] = sb.toString();
}
System.out.println(Arrays.toString(output));
OUTPUT:
[b9, ab9, b9b9, 99b99a, a9, aA9]
You want to use a very simple state machine. For each character you're looping through in the input string, keep track of a boolean. If the character is a 9, set the boolean to true. If the character is a letter add one to the letter and set the boolean to false. Then add the character to the output stringbuilder.
For input you use a Reader. For output use a StringBuilder.
Use a 1 token look ahead parser technique. Here is some psuedoish code:
for (int index = 0; index < buffer.length(); ++index)
{
if (index < buffer.length() - 1)
{
if (buffer.charAt(index + 1) == '9')
{
char current = buffer.charAt(index) + 1; // this is probably not the best technique for this.
buffer.setCharAt(index, current);
}
}
}
another solution is for example to use
StringUtils.indexOf(String str, char searchChar, int startPos)
in a way as Ernest Friedman-Hill pointed, take this as experimental example, not the most performant
(This is not homework)
We have some extra exercices we can do, and i have done some.
But i got stuck in this one...
I need to make a program that given the string "loool" prints "l:1:o:3:l:1".
I have tried a bunch of combinations but i keep getting the same problem:
- I cant make the last repeated letter to get print ( Because with my code the next char needs to be different for a print to occurr).
String str = "loool";
StringBuilder sb = new StringBuilder();
int count = 1;
char before;
before = str.charAt(0);
for (int i = 1;i < str.length();i++) {
if (str.charAt(i) == before) {
count++;
}
else {
sb.append(before + ":" + count);
before = str.charAt(i);
count = 1;
}
}
return sb.toString();
You need to add some logic after your loop has finished, in order to deal with this problem. This logic will probably be very similar to the some of the code that you're using in the else block.