Move spaces to front of string in single traversal

Given a string that has set of words and spaces, write a program to move all spaces to front of string, by traversing the string only once.

Examples:

Input  : str = "geeks for geeks"
Output : ste = "  geeksforgeeks"

Input  : str = "move these spaces to beginning"
Output : str = "    movethesespacestobeginning"
There were four space characters in input,
all of them should be shifted in front.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Method 1 (Using Swap)
Idea is to maintain two indices i and j. Traverse from end to beginning. If the current index contains space, swap chars in index i with index j. This will bring all spaces to beginning of the array.

C++

// CPP program to bring all spaces in front of 
// string using swapping technique 
#include<bits/stdc++.h> 
using namespace std; 
  
// Function to find spaces and move to beginning 
void moveSpaceInFront(char str[]) 
{ 
    // Traverse from end and swap spaces 
    int i = strlen(str)-1; 
    for (int j = i; j >= 0; j--) 
        if (str[j] != ' ') 
            swap(str[i--], str[j]); 
} 
  
// Driver code 
int main() 
{ 
    char str[] = "Hey there, it's GeeksforGeeks"; 
    moveSpaceInFront(str); 
    cout << str; 
    return 0; 
} 

Java

// Java program to bring all spaces in front of  
// string using swapping technique  
class GFG  
{ 
  
    // Function to find spaces and move to beginning  
    static void moveSpaceInFront(char str[])  
    {  
        // Traverse from end and swap spaces  
        int i = str.length-1;  
        for (int j = i; j >= 0; j--)  
            if (str[j] != ' ') 
            { 
                char c = str[i]; 
                str[i] = str[j]; 
                str[j] = c; 
                i--; 
            } 
    }     
  
    // Driver code  
    public static void main(String[] args) 
    { 
        char str[] = "Hey there, it's GeeksforGeeks".toCharArray();  
        moveSpaceInFront(str);  
        System.out.println(String.valueOf(str)); 
    } 
} 
  
// This code is contributed by  
// 29AjayKumar 

Python3

# Python3 program to bring all spaces  
# in front of string using swapping technique 
  
# Function to find spaces and move to beginning 
def moveSpaceInFront(s): 
  
    # Traverse from end and swap spaces 
    i = len(s) - 1; 
    for j in range(i, -1, -1): 
        if (s[j] != ' '): 
            s = swap(s, i, j); 
            i -= 1; 
    return s; 
      
def swap(c, i, j): 
    c = list(c) 
    c[i], c[j] = c[j], c[i] 
    return ''.join(c)  
      
# Driver code 
s = "Hey there, it's GeeksforGeeks"; 
s = moveSpaceInFront(s); 
print(s); 
  
# This code is contributed  
# by Princi Singh 

C#

// C# program to bring all spaces in front of  
// string using swapping technique  
using System; 
  
class GFG  
{ 
  
    // Function to find spaces and move to beginning  
    static void moveSpaceInFront(char []str)  
    {  
          
        // Traverse from end and swap spaces  
        int i = str.Length-1;  
        for (int j = i; j >= 0; j--)  
            if (str[j] != ' ') 
            { 
                char c = str[i]; 
                str[i] = str[j]; 
                str[j] = c; 
                i--; 
            } 
    }  
  
    // Driver code  
    public static void Main() 
    { 
        char []str = "Hey there, it's GeeksforGeeks".ToCharArray();  
        moveSpaceInFront(str);  
        Console.WriteLine(String.Join("",str)); 
    } 
} 
  
// This code is contributed by PrinciRaj1992 

Output:

   Heythere,it'sGeeksforGeeks

Time complexity-: O(n)
Auxiliary Space-: O(1)

Method 2 (Without using swap)
The idea is to copy all non-space characters to end. Finally copy spaces.

C++

// CPP program to bring all spaces in front of 
// string using swapping technique 
#include<bits/stdc++.h> 
using namespace std; 
  
// Function to find spaces and move to beginning 
void moveSpaceInFront(char str[]) 
{ 
     // Keep copying non-space characters 
     int i = strlen(str); 
     for (int j=i; j >= 0; j--) 
          if (str[j] != ' ') 
             str[i--] = str[j]; 
  
     // Move spaces to be beginning 
     while (i >= 0) 
         str[i--] = ' '; 
} 
  
// Driver code 
int main() 
{ 
    char str[] = "Hey there, it's GeeksforGeeks"; 
    moveSpaceInFront(str); 
    cout << str; 
    return 0; 
} 

Java

// Java program to bring all spaces in front of 
// string using swapping technique 
class GFG  
{ 
  
// Function to find spaces and move to beginning 
static void moveSpaceInFront(char str[]) 
{ 
    // Keep copying non-space characters 
    int i = str.length-1; 
      
    for (int j = i; j >= 0; j--) 
        if (str[j] != ' ') 
            str[i--] = str[j]; 
  
    // Move spaces to be beginning 
    while (i >= 0) 
        str[i--] = ' '; 
} 
  
// Driver code 
public static void main(String[] args)  
{ 
    char str[] = "Hey there, it's GeeksforGeeks".toCharArray(); 
    moveSpaceInFront(str); 
    System.out.println(String.valueOf(str)); 
} 
}  
  
// This code is contributed by Rajput-Ji 

Python3

# Python3 program to bring all spaces  
# in front of sing using swapping technique 
  
# Function to find spaces and  
# move to beginning 
def moveSpaceInFront(s): 
  
    # Keep copying non-space characters 
    i = len(s) - 1; 
      
    for j in range(i, -1, -1): 
        if (s[j] != ' '): 
            s = s[:i] + s[j] + s[i + 1:] 
            i -= 1; 
  
    # Move spaces to be beginning 
    while (i >= 0): 
        s = s[:i] + ' ' + s[i + 1:] 
        i -= 1
    return s; 
  
# Driver code 
s = "Hey there, it's GeeksforGeeks"; 
s = moveSpaceInFront(s); 
print(s); 
  
# This code is contributed  
# by Princi Singh  

C#

// C# program to bring all spaces in front of  
// string using swapping technique 
using System; 
  
class GFG  
{  
  
// Function to find spaces and move to beginning  
static void moveSpaceInFront(char []str)  
{  
    // Keep copying non-space characters  
    int i = str.Length-1;  
      
    for (int j = i; j >= 0; j--)  
        if (str[j] != ' ')  
            str[i--] = str[j];  
  
    // Move spaces to be beginning  
    while (i >= 0)  
        str[i--] = ' ';  
}  
  
// Driver code  
public static void Main(String[] args)  
{  
    char []str = "Hey there, it's GeeksforGeeks". 
                                    ToCharArray();  
    moveSpaceInFront(str);  
    Console.WriteLine(String.Join("",str));  
}  
}  
  
// This code is contributed by Rajput-Ji  

Output:

   Heythere,it'sGeeksforGeeks

Time complexity-: O(n)
Auxiliary Space -:O(1)

This article is contributed by SAKSHI TIWARI. If you like GeeksforGeeks(We know you do!) and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

C++

Java

Python3

C#

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