Reverse words in a given string

Difficulty Level : Medium
Last Updated : 13 Feb, 2023

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Given a string, the task is to reverse the order of the words in the given string.

Examples:

Input: s = “geeks quiz practice code”
Output: s = “code practice quiz geeks”

Input: s = “i love programming very much”
Output: s = “much very programming love i”

Approach:

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.

Follow the below steps to solve the problem:

Run a for loop to traverse the string and create a temporary string to store the words
If the current character is a space then add the current string to the answer and empty the string
Else push the character into the string
Print the answer array in reverse order

Below is the implementation of the above approach:

C++

// C++ 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;
 
    // Driver code
    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 ";
 
        // Function call
        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

Javascript

<script>
    // Javascript program to 
    // reverse a String
     
    // Reverse the letters 
    // of the word 
    function reverse(str,start,end)
    {
        // Temporary variable 
        // to store character 
        let 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
    function reverseWords(s)
    {
        // Reversing individual words as
        // explained in the first step
        s=s.split("");
        let start = 0;
        for (let 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.join("");
    }
    // Driver Code
    var s = "i like this program very much ";
     
     
    document.write(reverseWords(s));
     
    // This code is contributed by avanitrachhadiya2155
</script>

Output

much very program this like i

Time complexity: O(N)
Auxiliary Space: O(N)

Note: The above code doesn’t handle the cases when the string starts with space.

Below is the implementation of the approach that 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 to reverse a string
#include <bits/stdc++.h>
using namespace std;
 
// Function to reverse any sequence
// starting with pointer begin and
// ending with pointer end
void reverse(string& s, int begin, int end)
{
 
    while (begin < end) {
        swap(s[begin++], s[end--]);
    }
}
 
// C++ program for above approach
 
void reverseWords(string& s)
{
    int word_begin = -1;
 
    //  /* temp is for word boundary */
    int i = 0;
 
    /*STEP 1 of the above algorithm */
    while (i < s.size()) {
 
        /*This condition is to make sure that the
          string start with valid character (not
          space) only*/
        if ((word_begin == -1) && (s[i] != ' ')) {
            word_begin = i;
        }
        if (word_begin != -1
            && ((s[i + 1] == ' ') || (i + 1 == s.size()))) {
            reverse(s, word_begin, i);
            word_begin = -1;
        }
        i++;
    } /* End of while */
 
    /*STEP 2 of the above algorithm */
    reverse(s, 0, s.size() - 1);
}
 
// Driver Code
int main()
{
    string s = "i like this program very much";
 
    // Function call
    reverseWords(s);
    cout << s << endl;
    ;
    return 0;
}
 
// This code is contributed by garg28harsh.

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;
    }
}
 
// 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);
}
 
// Driver Code
int main()
{
    char s[] = "i like this program very much";
    char* temp = s;
   
      // Function call
    reverseWords(s);
    printf("%s", s);
    return 0;
}

Java

// Java program to reverse a string
import java.io.*;
 
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--;
    }
  }
 
  static char[] reverseWords(char[] s)
  {
    int word_begin = -1;
 
    //  /* temp is for word boundary */
    int i = 0;
 
    /*STEP 1 of the above algorithm */
    while (i < s.length) {
 
      /*This condition is to make sure that the
              string start with valid character (not
              space) only*/
      if ((word_begin == -1) && (s[i] != ' ')) {
        word_begin = i;
      }
      if (word_begin != -1
          && ((i + 1 == s.length)
              || (s[i + 1] == ' '))) {
        reverse(s, word_begin, i);
        word_begin = -1;
      }
      i++;
    } /* End of while */
 
    /*STEP 2 of the above algorithm */
    reverse(s, 0, (s.length - 1));
    return s;
  }
 
  // Driver Code
  public static void main(String[] args)
  {
    String s = "i like this program very much";
 
    // Function call
    char[] p = reverseWords(s.toCharArray());
    System.out.println(p);
  }
}
 
// This code is contributed by Srj_27.

Python3

# Python3 program to reverse a string
 
# Reverse the letters
# of the word
def reverse(str, start, end):
    # Temporary variable
    # to store character
    temp = ''
    str1 = ""
 
    while (start <= end):
        # Swapping the first
        # and last character
        temp = str[start]
        str[start] = str[end]
        str[end] = temp
        start+=1
        end-=1
    return str1.join(str)
 
def reverseWords(s):
     
    word_begin = -1
 
    #  temp is for word boundary 
    i = 0
 
    # STEP 1 of the above algorithm 
    while (i < len(s)):
 
        ''' This condition is to make sure that the
                string start with valid character (not
                space) only '''
        if ((word_begin == -1) and (s[i] != ' ')):
            word_begin = i
        if (word_begin != -1 and ((i + 1 == len(s)) or (s[i + 1] == ' '))):
            s = reverse(list(s), word_begin, i)
            word_begin = -1
        i+=1
    ''' End of while '''
 
    # STEP 2 of the above algorithm 
    s = reverse(list(s), 0, (len(s) - 1))
    return s
 
# Driver Code
s = "i like this program very much"
 
# Function call
p = reverseWords(list(s))
print(p)
 
# This code is contributed by akashish__

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--;
    }
  }
 
  static char[] reverseWords(char[] s)
  {
    int word_begin = -1;
 
    //  /* temp is for word boundary */
    int i = 0;
 
    /*STEP 1 of the above algorithm */
    while (i < s.Length) {
 
      /*This condition is to make sure that the
                    string start with valid character (not
                    space) only*/
      if ((word_begin == -1) && (s[i] != ' ')) {
        word_begin = i;
      }
      if (word_begin != -1
          && ((i + 1 == s.Length)
              || (s[i + 1] == ' '))) {
        reverse(s, word_begin, i);
        word_begin = -1;
      }
      i++;
    } /* End of while */
 
    /*STEP 2 of the above algorithm */
    reverse(s, 0, (s.Length - 1));
    return s;
  }
 
  // Driver Code
  static void Main(string[] args)
  {
    String s = "i like this program very much";
 
    // Function call
    char[] p = reverseWords(s.ToCharArray());
    Console.WriteLine(p);
  }
}
 
// This code is contributed by Karandeep1234.

Javascript

// Function to reverse any sequence
// starting with pointer begin and
// ending with pointer end
function reverse(s, begin, end) {
    while (begin < end) {
        let charArray = [...s];
        let temp = charArray[begin];
        charArray[begin] = charArray[end];
        charArray[end] = temp;
        begin++;
        end--;
        s = charArray.join("");
    }
    return s;
}
 
function reverseWords(s) {
    let word_begin = -1;
 
    //  /* temp is for word boundary */
    let i = 0;
 
    /*STEP 1 of the above algorithm */
    while (i < s.length) {
 
        /*This condition is to make sure that the
          string start with valid character (not
          space) only*/
        if ((word_begin == -1) && (s[i] != ' ')) {
            word_begin = i;
        }
        if (word_begin != -1
            && ((s[i + 1] == ' ') || (i + 1 == s.length))) {
            s = reverse(s, word_begin, i);
            word_begin = -1;
        }
        i++;
    } /* End of while */
 
    /*STEP 2 of the above algorithm */
    s = reverse(s, 0, s.length - 1);
    return s;
}
 
// Driver Code
let s = "i like this program very much";
 
// Function call
s = reverseWords(s);
console.log(s);
 
 
// This code is contributed by akashish__

Output

much very program this like i

Time Complexity: O(N)
Auxiliary Space: O(N)

Approach: To solve the problem follow the below idea:

We can do the above task by splitting and saving the string in a reverse manner.

Follow the below steps to solve the problem:

Store the string in the form of words
Run a for loop in reverse order to print the words accordingly

Below is the implementation of the above approach:

C++

// C++ program to reverse a string
// s = input()
 
#include <bits/stdc++.h>
using namespace std;
 
int main()
{
    string s[] = { "i",       "like", "this",
                   "program", "very", "much" };
 
    string ans = "";
    for (int i = 5; i >= 0; i--) {
        ans += s[i] + " ";
    }
  
    cout << (ans.substr(0, ans.length() - 1)) << endl;
 
    return 0;
}

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(
            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(" ".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(ans.Substring(0, ans.Length - 1));
    }
}

Javascript

<script>
 
// JavaScript program to reverse a string
 
var s= ["i", "like", "this", "program", "very", "much"];
                                         
    var ans ="";
    for (var i = 5; i >= 0; i--)
    {
        ans += s[i] + " ";
    }
     
    document.write(ans.slice(0,ans.length-1));
 
 
</script>

Output

much very program this like i

Time Complexity: O(N)
Auxiliary Space: O(N)