Reverse the ordering of words in a string

Question

I have this string s1 = \"My name is X Y Z\" and I want to reverse the order of the words so that s1 = \"Z Y X is name My\".

I can do it u

Answer 1

Reverse the entire string, then reverse the letters of each individual word.

After the first pass the string will be

s1 = "Z Y X si eman yM"

and after the second pass it will be

s1 = "Z Y X is name My"

Answer 2

In Python, if you can't use [::-1] or reversed(), here is the simple way:

def reverse(text):

  r_text = text.split(" ")
  res = []
  for word in range(len(r_text) - 1, -1, -1): 
    res.append(r_text[word])

  return " ".join(res)

print (reverse("Hello World"))

>> World Hello
[Finished in 0.1s]

Answer 3

This quick program works..not checks the corner cases though.

#include <stdio.h>
#include <stdlib.h>
struct node
{
    char word[50];
    struct node *next;
};
struct stack
{
    struct node *top;
};
void print (struct stack *stk);
void func (struct stack **stk, char *str);
main()
{
    struct stack *stk = NULL;
    char string[500] = "the sun is yellow and the sky is blue";
    printf("\n%s\n", string);
    func (&stk, string);
    print (stk);
}
void func (struct stack **stk, char *str)
{
    char *p1 = str;
    struct node *new = NULL, *list = NULL;
    int i, j;
    if (*stk == NULL)
    {
        *stk = (struct stack*)malloc(sizeof(struct stack));
        if (*stk == NULL)
            printf("\n####### stack is not allocated #####\n");
        (*stk)->top = NULL;
    }
    i = 0;
    while (*(p1+i) != '\0')
    {
        if (*(p1+i) != ' ')
        {
            new = (struct node*)malloc(sizeof(struct node));
            if (new == NULL)
                printf("\n####### new is not allocated #####\n");
            j = 0;
            while (*(p1+i) != ' ' && *(p1+i) != '\0')
            {
                new->word[j] = *(p1 + i);
                i++;
                j++;
            }
            new->word[j++] = ' ';
            new->word[j] = '\0';
            new->next = (*stk)->top;
            (*stk)->top = new;
        }
        i++;
   }
}
void print (struct stack *stk)
{
    struct node *tmp = stk->top;
    int i;
    while (tmp != NULL)
    {
        i = 0;
        while (tmp->word[i] != '\0')
        {
            printf ("%c" , tmp->word[i]);
            i++;
        }
        tmp = tmp->next;
    }
    printf("\n");
}

Answer 4

This is assuming all words are separated by spaces:

#include <stdio.h>
#include <string.h>

int main()
{
    char string[] = "What are you looking at";
    int i, n = strlen(string);

    int tail = n-1;
    for(i=n-1;i>=0;i--)
    {
        if(string[i] == ' ' || i == 0)
        {
            int cursor = (i==0? i: i+1);
            while(cursor <= tail)
                printf("%c", string[cursor++]);
            printf(" ");
            tail = i-1;
        }
    }
    return 0;
}

Answer 5

It can be done more simple using sscanf:

void revertWords(char *s);
void revertString(char *s, int start, int n);
void revertWordsInString(char *s);

void revertString(char *s, int start, int end)
{
     while(start<end)
     {
         char temp = s[start];
         s[start] = s[end];
         s[end]=temp;
         start++;
         end --;
     }
}


void revertWords(char *s)
{
  int start = 0;

  char *temp = (char *)malloc(strlen(s) + 1);
  int numCharacters = 0;
  while(sscanf(&s[start], "%s", temp) !=EOF)
  {
      numCharacters = strlen(temp);

      revertString(s, start, start+numCharacters -1);
      start = start+numCharacters + 1;
      if(s[start-1] == 0)
      return;

  }
  free (temp);

}

void revertWordsInString(char *s)
{
   revertString(s,0, strlen(s)-1);
   revertWords(s);
}

int main()
{
   char *s= new char [strlen("abc deff gh1 jkl")+1];
   strcpy(s,"abc deff gh1 jkl");
   revertWordsInString(s);
   printf("%s",s);
   return 0;
}

Answer 6

public class manip{

public static char[] rev(char[] a,int left,int right) {
    char temp;
    for (int i=0;i<(right - left)/2;i++)    {
        temp = a[i + left];
        a[i + left] = a[right -i -1];
        a[right -i -1] = temp;
    }

    return a;
}
public static void main(String[] args) throws IOException {

    String s= "i think this works";
    char[] str = s.toCharArray();       
    int i=0;
    rev(str,i,s.length());
    int j=0;
    while(j < str.length) {
        if (str[j] != ' ' && j != str.length -1) {
            j++;
        } else
        {
            if (j == (str.length -1))   {
                j++;
            }
            rev(str,i,j);
            i=j+1;
            j=i;
        }
    }
    System.out.println(str);
}