Reversing characters in each word in a sentence -

Question

This code is inside the main function:

Scanner input = new Scanner(System.in);

System.out.println("Type a sentence");
String sentence = input.next();

Stack<Character> stk = new Stack<Character>();
int i = 0;

while (i < sentence.length())
{
    while (sentence.charAt(i) != ' ' && i < sentence.length() - 1)
    {
        stk.push(sentence.charAt(i));
        i++;
    }
    stk.empty();
    i++;
}

And this is the empty() function:

public void empty()
{
    while (this.first != null)
        System.out.print(this.pop());
}

It doesn't work properly, as by typing example sentence I am getting this output: lpmaxe. The first letter is missing and the loop stops instead of counting past the space to the next part of the sentence.

I am trying to achieve this:

This is a sentence ---> sihT si a ecnetnes

Answer 1

public class reverseStr {
public static void main(String[] args) {
    String testsa[] = { "", " ", "       ", "a ", " a", " aa bd  cs " };
    for (String tests : testsa) {
        System.out.println(tests + "|" + reverseWords2(tests) + "|");
    }
}

public static String reverseWords2(String s) {
    String[] sa;
    String out = "";
    sa = s.split(" ");
    for (int i = 0; i < sa.length; i++) {
        String word = sa[sa.length - 1 - i];
        // exclude "" in splited array
        if (!word.equals("")) {
            //add space between two words
            out += word + " ";
        }
    }
    //exclude the last space and return when string is void
    int n = out.length();
    if (n > 0) {
        return out.substring(0, out.length() - 1);
    } else {
        return "";
    }
}

}

This can pass in leetcode

Answer 2

public class ReverseofeachWordinaSentance {

/**
 * @param args
 */
public static void main(String[] args) {
    String source = "Welcome to the word reversing program";

    for (String str : source.split(" ")) {
        System.out.print(new StringBuilder(str).reverse().toString());
        System.out.print(" ");
    }
System.out.println("");

    System.out.println("------------------------------------ ");
    String original = "Welcome to the word reversing program";
    wordReverse(original);
    System.out.println("Orginal Sentence :::: "+original);
    System.out.println("Reverse Sentence :::: "+wordReverse(original));
}

public static String wordReverse(String original){

    StringTokenizer string = new StringTokenizer(original);

    Stack<Character> charStack = new Stack<Character>();

    while (string.hasMoreTokens()){

    String temp = string.nextToken();

    for (int i = 0; i < temp.length(); i ++){

    charStack.push(temp.charAt(i));
}
    charStack.push(' ');
}

    StringBuilder result = new StringBuilder();
    while(!charStack.empty()){
    result.append(charStack.pop());
}

    return result.toString();   
}

}

Answer 3

Per modifications to the original post, where the OP is now indicating that his goal is to reverse the letter order of the words within a sentence, but to leave the words in their initial positions.

The simplest way to do this, I think, is to make use of the String split function, iterate through the words, and reverse their orders.

String[] words = sentence.split(" "); // splits on the space between words

for (int i = 0; i < words.length; i++) {
    String word = words[i];
    System.out.print(reverseWord(word));

    if (i < words.length-1) {
        System.out.print(" "); // space after all words but the last
    }
}

Where the method reverseWord is defined as:

public String reverseWord(String word) {
    for( int i = 0; i < word.length(); i++) {
        stk.push(word.charAt(i));
    }
    return stk.empty();
}

And where the empty method has been changed to:

public String empty() {
    String stackWord = "";
    while (this.first != null)
        stackWord += this.pop();
    return stackWord;
}

Original response

The original question indicated that the OP wanted to completely reverse the sentence.

You've got a double-looping construct where you don't really need it.

Consider this logic:

1. Read each character from the input string and push that character to the stack
2. When the input string is empty, pop each character from the stack and print it to screen.

So:

for( int i = 0; i < sentence.length(); i++) {
    stk.push(sentence.charAt(i));
}
stk.empty();

Answer 4

I assume that what you want your code to do is to reverse each word in turn, not the entire string. So, given the input example sentence you want it to output elpmaxe ecnetnes not ecnetnes elpmaxe.

The reason that you see lpmaxe instead of elpmaxe is because your inner while-loop doesn't process the last character of the string since you have i < sentence.length() - 1 instead of i < sentence.length(). The reason that you only see a single word is because your sentence variable consists only of the first token of the input. This is what the method Scanner.next() does; it reads the next (by default) space-delimited token.

If you want to input a whole sentence, wrap up System.in as follows:

BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

and call reader.readLine().

Hope this helps.

Answer 5

Assuming you've already got your input in sentence and the Stack object is called stk, here's an idea:

char[] tokens = sentence.toCharArray();
for (char c : tokens) {
    if (c == ' ') {
        stk.empty();
        System.out.print(c);
    } else  {
        stk.add(c);
    }
}

Thus, it will scan through one character at a time. If we hit a space character, we'll assume we've hit the end of a word, spit out that word in reverse, print that space character, then continue. Otherwise, we'll add the character to the stack and continue building the current word. (If you want to also allow punctuation like periods, commas, and the like, change if (c == ' ') { to something like if (c == ' ' || c == '.' || c == ',') { and so on.)

As for why you're only getting one word, darrenp already pointed it out. (Personally, I'd use a Scanner instead of a BufferedReader unless speed is an issue, but that's just my opinion.)

Answer 6

import java.util.StringTokenizer;
public class stringWork {
public static void main(String[] args) {
    String s1 = "Hello World";
    s1 = reverseSentence(s1);
    System.out.println(s1);
    s1 = reverseWord(s1);
    System.out.println(s1);
}
private static String reverseSentence(String s1){
    String s2 = "";
    for(int i=s1.length()-1;i>=0;i--){
        s2 += s1.charAt(i);
    }
    return s2;
}
private static String reverseWord(String s1){
    String s2 = "";
    StringTokenizer st = new StringTokenizer(s1);
    while (st.hasMoreTokens()) {
        s2 += reverseSentence(st.nextToken());
        s2 += " ";
    }
    return s2;
}

}