Example: Let the input string be “i like this program very much”. The function should change the string to “much very program this like i”
Examples:
Input: s = “geeks quiz practice code”
Output: s = “code practice quiz geeks”Input: s = “getting good at coding needs a lot of practice”
Output: s = “practice of lot a needs coding at good getting”
Algorithm:
- Initially, reverse the individual words of the given string one by one, for the above example, after reversing individual words the string should be “i ekil siht margorp yrev hcum”.
- Reverse the whole string from start to end to get the desired output “much very program this like i” in the above example.
Below is the implementation of the above approach:
C++
// CPP program to reverse a string #include <bits/stdc++.h> using namespace std; // Function to reverse words*/ void reverseWords(string s) { // temporary vector to store all words vector<string> tmp; string str = "" ; for ( int i = 0; i < s.length(); i++) { // Check if we encounter space // push word(str) to vector // and make str NULL if (s[i] == ' ' ) { tmp.push_back(str); str = "" ; } // Else add character to // str to form current word else str += s[i]; } // Last word remaining,add it to vector tmp.push_back(str); // Now print from last to first in vector int i; for (i = tmp.size() - 1; i > 0; i--) cout << tmp[i] << " " ; // Last word remaining,print it cout << tmp[0] << endl; } // Driver Code int main() { string s = "i like this program very much" ; reverseWords(s); return 0; } |
C
// C program to reverse a string #include <stdio.h> // Function to reverse any sequence // starting with pointer begin and // ending with pointer end void reverse( char * begin, char * end) { char temp; while (begin < end) { temp = *begin; *begin++ = *end; *end-- = temp; } } // Function to reverse words*/ void reverseWords( char * s) { char * word_begin = s; // Word boundary char * temp = s; // Reversing individual words as // explained in the first step while (*temp) { temp++; if (*temp == '\0' ) { reverse(word_begin, temp - 1); } else if (*temp == ' ' ) { reverse(word_begin, temp - 1); word_begin = temp + 1; } } // Reverse the entire string reverse(s, temp - 1); } // Driver Code int main() { char s[] = "i like this program very much" ; char * temp = s; reverseWords(s); printf ( "%s" , s); return 0; } |
Java
// Java program to // reverse a String import java.util.*; class GFG{ // Reverse the letters // of the word static void reverse( char str[], int start, int end) { // Temporary variable // to store character char temp; while (start <= end) { // Swapping the first // and last character temp = str[start]; str[start] = str[end]; str[end] = temp; start++; end--; } } // Function to reverse words static char [] reverseWords( char []s) { // Reversing individual words as // explained in the first step int start = 0 ; for ( int end = 0 ; end < s.length; end++) { // If we see a space, we // reverse the previous // word (word between // the indexes start and end-1 // i.e., s[start..end-1] if (s[end] == ' ' ) { reverse(s, start, end); start = end + 1 ; } } // Reverse the last word reverse(s, start, s.length - 1 ); // Reverse the entire String reverse(s, 0 , s.length - 1 ); return s; } // Driver Code public static void main(String[] args) { String s = "i like this program very much " ; char []p = reverseWords(s.toCharArray()); System.out.print(p); } } // This code is contributed by gauravrajput1 |
Python3
# Python3 program to reverse a string # Function to reverse each word in the string def reverse_word(s, start, end): while start < end: s[start], s[end] = s[end], s[start] start = start + 1 end - = 1 s = "i like this program very much" # Convert string to list to use it as a char array s = list (s) start = 0 while True : # We use a try catch block because for # the last word the list.index() function # returns a ValueError as it cannot find # a space in the list try : # Find the next space end = s.index( ' ' , start) # Call reverse_word function # to reverse each word reverse_word(s, start, end - 1 ) #Update start variable start = end + 1 except ValueError: # Reverse the last word reverse_word(s, start, len (s) - 1 ) break # Reverse the entire list s.reverse() # Convert the list back to # string using string.join() function s = "".join(s) print (s) # Solution contributed by Prem Nagdeo |
C#
// C# program to // reverse a String using System; class GFG { // Reverse the letters // of the word static void reverse( char []str, int start, int end) { // Temporary variable // to store character char temp; while (start <= end) { // Swapping the first // and last character temp = str[start]; str[start] = str[end]; str[end] = temp; start++; end--; } } // Function to reverse words static char [] reverseWords( char []s) { // Reversing individual words as // explained in the first step int start = 0; for ( int end = 0; end < s.Length; end++) { // If we see a space, we // reverse the previous // word (word between // the indexes start and end-1 // i.e., s[start..end-1] if (s[end] == ' ' ) { reverse(s, start, end); start = end + 1; } } // Reverse the last word reverse(s, start, s.Length - 1); // Reverse the entire String reverse(s, 0, s.Length - 1); return s; } // Driver Code public static void Main(String[] args) { String s = "i like this program very much " ; char []p = reverseWords(s.ToCharArray()); Console.Write(p); } } // This code is contributed by jana_sayantan |
much very program this like i
The above code doesn’t handle the cases when the string starts with space. The following version handles this specific case and doesn’t make unnecessary calls to reverse function in the case of multiple spaces in between. Thanks to rka143 for providing this version.
C
// C program for above approach: void reverseWords( char * s) { char * word_begin = NULL; // /* temp is for word boundary */ char * temp = s; /*STEP 1 of the above algorithm */ while (*temp) { /*This condition is to make sure that the string start with valid character (not space) only*/ if ((word_begin == NULL) && (*temp != ' ' )) { word_begin = temp; } if (word_begin && ((*(temp + 1) == ' ' ) || (*(temp + 1) == '\0' ))) { reverse(word_begin, temp); word_begin = NULL; } temp++; } /* End of while */ /*STEP 2 of the above algorithm */ reverse(s, temp - 1); } |
Time Complexity: O(n)
Another Approach:
we can do the above task by splitting and saving the string in a reverse manner.
Below is the implementation of the above approach:
Java
// Java program to reverse a string // s = input() public class ReverseWords { public static void main(String[] args) { String s[] = "i like this program very much" . split( " " ); String ans = "" ; for ( int i = s.length - 1 ; i >= 0 ; i--) { ans += s[i] + " " ; } System.out.println( "Reversed String:" ); System.out.println(ans.substring( 0 , ans.length() - 1 )); } } |
Python3
# Python3 program to reverse a string # s = input() s = "i like this program very much" words = s.split( ' ' ) string = [] for word in words: string.insert( 0 , word) print ( "Reversed String:" ) print ( " " .join(string)) # Solution proposed bu Uttam |
C#
// C# program to reverse a string // s = input() using System; public class ReverseWords { public static void Main() { string [] s = "i like this program very much" . Split( ' ' ); string ans = "" ; for ( int i = s.Length - 1; i >= 0; i--) { ans += s[i] + " " ; } Console.Write( "Reversed String:\n" ); Console.Write(ans.Substring(0, ans.Length - 1)); } } |
Reversed String: much very program this like i
Time Complexity: O(n)
Without using any extra space:
The above task can also be accomplished by splitting and directly swapping the string starting from the middle. As direct swapping is involved, less space is consumed too.
Below is the implementation of the above approach:
Java
// Java code to reverse a string class GFG{ // Reverse the string public static String[] RevString(String[] s, int l) { // Check if number of words is even if (l % 2 == 0 ) { // Find the middle word int j = l / 2 ; // Starting from the middle // start swapping words at // jth position and l-1-j position while (j <= l - 1 ) { String temp; temp = s[l - j - 1 ]; s[l - j - 1 ] = s[j]; s[j] = temp; j += 1 ; } } // Check if number of words is odd else { // Find the middle word int j = (l / 2 ) + 1 ; // Starting from the middle start // swapping the words at jth // position and l-1-j position while (j <= l - 1 ) { String temp; temp = s[l - j - 1 ]; s[l - j - 1 ] = s[j]; s[j] = temp; j += 1 ; } } // Return the reversed sentence return s; } // Driver Code public static void main(String[] args) { String s = "getting good at coding " + "needs a lot of practice" ; String[] words = s.split( "\\s" ); words = RevString(words, words.length); s = String.join( " " , words); System.out.println(s); } } // This code is contributed by MuskanKalra1 |
Python3
# Python3 code to reverse a string # Reverse the string def RevString(s,l): # Check if number of words is even if l % 2 = = 0 : # Find the middle word j = int (l / 2 ) # Starting from the middle # start swapping words # at jth position and l-1-j position while (j < = l - 1 ): s[j], s[l - j - 1 ] = s[l - j - 1 ], s[j] j + = 1 # Check if number of words is odd else : # Find the middle word j = int (l / 2 + 1 ) # Starting from the middle # start swapping the words # at jth position and l-1-j position while (j < = l - 1 ): s[j], s[l - 1 - j] = s[l - j - 1 ], s[j] j + = 1 # return the reversed sentence return s; # Driver Code s = 'getting good at coding needs a lot of practice' string = s.split( ' ' ) string = RevString(string, len (string)) print ( " " .join(string)) |
C#
// C# code to reverse a string using System; class GFG{ // Reverse the string public static String[] RevString(String[] s, int l) { // Check if number of words is even if (l % 2 == 0) { // Find the middle word int j = l / 2; // Starting from the middle // start swapping words at // jth position and l-1-j position while (j <= l - 1) { String temp; temp = s[l - j - 1]; s[l - j - 1] = s[j]; s[j] = temp; j += 1; } } // Check if number of words is odd else { // Find the middle word int j = (l / 2) + 1; // Starting from the middle start // swapping the words at jth // position and l-1-j position while (j <= l - 1) { String temp; temp = s[l - j - 1]; s[l - j - 1] = s[j]; s[j] = temp; j += 1; } } // Return the reversed sentence return s; } // Driver Code public static void Main(String[] args) { String s = "getting good at coding " + "needs a lot of practice" ; String[] words = s.Split( "\\s" ); words = RevString(words, words.Length); s = String.Join( " " , words); Console.WriteLine(s); } } // This code is contributed by shivanisinghss2110 |
practice of lot a needs coding at good getting
Please write comments if you find any bug in the above code/algorithm, or find other ways to solve the same problem.
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