Reverse a given sentence in java

Question

This was the question asked me in amazon interview. , Write a program to reverse a given sentence like "This is interview question" the output must be "question interview is this".Can any tell me how to get this done?

Thanks in advance

Answer 1

You split the string by the space then iterate over it backwards to assemble the reversed sentence.

string[] words =  "This is interview question".split(" ");

string rev = "";
for(int i = words.length - 1; i >= 0 ; i--)
{
   rev += words[i] + " ";
}

// rev = "question interview is This "

// can also use StringBuilder:
StringBuilder revb = new StringBuilder;
for(int i = words.length - 1; i >= 0 ; i--)
{
   revb.Append(words[i]);
   revb.Append(" ");
}
// revb.toString() = "question interview is This "

Answer 2

Just split it on a space character into a string array, then loop over the array in reverse order and construct the output string.

String input = "This is interview question";
String output = "";
String[] array = input.split(" ");
for(int i = array.length-1; i >= 0; i--)
{
    output += array[i];
    if (i != 0) { output += " "; }
}

Answer 3

String[] words = sentence.split(" ");
String[] reversedWords = ArrayUtils.reverse(words);
String reversedSentence = ArrayUtils.join(reversedWords, " ");

(using ArrayUtils from commons-lang, but these are easy methods to write - just a few loops)

Answer 4

Bozho already gave a great Java-specific answer, but in the event you ever need to solve this problem without Java API methods:

To reverse, you can simply pop individual words onto a stack and pop them all back off when there are no words left.

(Just to be extra clear, Java does provide a Stack class, so it is possible to use this method in Java as well).

Answer 5

a every boring bit of java:

List<String> l = new ArrayList<String>(Arrays.asList("this is an interview question".split("\\s")));
Collections.reverse(l);
StringBuffer b = new StringBuffer();
for( String s : l ){
    b.append(s).append(' ');
}
b.toString().trim();

in groovy it's a little bit more readable:

"this is an interview question"
    .split("\\s")
    .reverse()
    .join(' ')

Answer 6

Just being different: a recursive solution. Doesn't add any extra spaces.

public static String reverse(String s) {
   int k = s.indexOf(" ");
   return k == -1 ? s : reverse(s.substring(k + 1)) + " " + s.substring(0, k);
}


System.out.println("[" + reverse("This is interview question") + "]");
// prints "[question interview is This]"

---

I will also improve on the split solution by using \b instead (it's so obvious!).

    String[] parts = "Word boundary is better than space".split("\\b");
    StringBuilder sb = new StringBuilder();
    for (int i = parts.length; i --> 0 ;) {
        sb.append(parts[i]);
    }
    System.out.println("[" + sb.toString() + "]");
    // prints "[space than better is boundary Word]"

Answer 7

I also give it a try: Here's a version using a stack and a scanner:

String input = "this is interview question";
Scanner sc = new Scanner(input);
Stack<String> stack = new Stack<String>();

while(sc.hasNext()) {
    stack.push(sc.next());
}

StringBuilder output = new StringBuilder();

for(;;) { // forever
    output.append(stack.pop());

    if(stack.isEmpty()) {
        break; // end loop
    } else {
        output.append(" ");
    }
}

Answer 8

public class ReverseString {

    public void reverse(String[] source) {

        String dest = "";
        for (int n = source.length - 1; n >= 0; n--) {
            dest += source[n] + " ";
        }
        System.out.println(dest);

    }

    public static void main(String args[]) {
        ReverseString rs = new ReverseString();
        String[] str = "What is going on".split(" ");
        rs.reverse(str);

    }

}