Insert a Character in a Rotated String

Given an array of characters arr[] of size N and an integer K. You have to insert the characters into an empty string one by one such that every insertion is done after K positions to the right from the previous insertion and the string is circular. The task is to find the character after which the last insertion is done

Examples:

Input: arr[] = {‘1’, ‘2’, ‘3’, ‘4’, ‘5’}, K = 2 
Output: 1 
After the first insertion string becomes “1” 
After the second insertion string becomes “12” 
After third insertion, as the previous insertion was at position 2. 
So, the current insertion has to be at 2 + 2 i.e. 4th position. 
Since, the string is circular so moving 2 positions to the right will 
be “1|2” -> “12|” and the final string will be “123” 
After the fourth insertion, “123” -> “1|23” -> “12|3” i.e. “1243” 
After the fifth insertion, “1243” -> “1243|” -> “1|243” i.e. “15243” 
The last character inserted after the character ‘1’ 

Input: arr[] = {‘1’, ‘2’, ‘3’, ‘4’, ‘5’}, K = 1 
Output: 1 
Final string is “15324” 

Approach: For every character, insert it in the required position and also keep track of the previous position and the character after which the previous insertion was done. When all the characters have been inserted, print the character after which the last insertion was done.

Below is the implementation of the above approach: 

C++

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;

// Function to insert the character
char Insert(char arr[], int n, int k)
{
    // To store last position where
    // the insertion is done
    int ind = 0;

    // To store size of the string
    int sz = 0;

    // To store the modified string
    string s = "";

    // To store characters
    char ch = arr[0];

    // Add first character to the string
    s += ch;

    // Update the size
    sz = 1;

    // Update the index of last insertion
    ind = 0;

    // Insert all other characters to the string
    for (int i = 1; i < n; i++) {

        // Take the character
        ch = arr[i];

        // Take substring upto ind
        string s1 = s.substr(0, ind + 1);

        // Take modulo value of k with
        // the size of the string
        int temp = k % sz;

        // Check if we need to move to
        // the start of the string
        int ro = temp - min(temp, sz - ind - 1);

        // If we don't need to move to start of the string
        if (ro == 0) {

            // Take substring from upto temp
            string s2 = s.substr(ind + 1, temp);

            // Take substring which will be after
            // the inserted character
            string s3 = s.substr(ind + temp + 1,
                                 sz - ind - temp - 1);

            // Insert into the string
            s = s1 + s2 + ch + s3;

            // Store new inserted position
            ind = s1.size() + s2.size();

            // Store size of the new string
            // Technically sz + 1
            sz = s.size();
        }

        // If we need to move to start of the string
        else {

            // Take substring which will before
            // the inserted character
            string s2 = s.substr(0, ro);

            // Take substring which will be after
            // the inserted character
            string s3 = s.substr(ro, sz - ro);

            // Insert into the string
            s = s2 + ch + s3;

            // Store new inserted position
            ind = s2.size();

            // Store size of the new string
            // Technically sz + 1
            sz = s.size();
        }
    }

    // Return the required character
    if (ind == 0)
        return s[sz - 1];
    else
        return s[ind - 1];
}

// Driver code
int main()
{
    char arr[] = { '1', '2', '3', '4', '5' };

    int k = 2;

    int n = sizeof(arr) / sizeof(arr[0]);

    // Function call
    cout << Insert(arr, n, k);

    return 0;
}

Java

// Java implementation of the approach
import java.util.*;

class GFG{

// Function to insert the character
public static char Insert(char arr[], int n, int k)
{

    // To store last position where
    // the insertion is done
    int ind = 0;

    // To store size of the string
    int sz = 0;

    // To store the modified string
    String s = "";

    // To store characters
    char ch = arr[0];

    // Add first character to the string
    s += ch;

    // Update the size
    sz = 1;

    // Update the index of last insertion
    ind = 0;

    // Insert all other characters to the string
    for(int i = 1; i < n; i++)
    {

        // Take the character
        ch = arr[i];

        // Take substring upto ind
        String s1 = s.substring(0, ind + 1);

        // Take modulo value of k with
        // the size of the string
        int temp = k % sz;

        // Check if we need to move to
        // the start of the string
        int ro = temp - Math.min(temp, sz - ind - 1);

        // If we don't need to move to
        // start of the string
        if (ro == 0)
        {

            // Take substring from upto temp
            String s2 = s.substring(ind + 1,
                                    ind + 1 + temp);

            // Take substring which will be after
            // the inserted character
            String s3 = s.substring(ind + temp + 1, sz);

            // Insert into the string
            s = s1 + s2 + ch + s3;

            // Store new inserted position
            ind = s1.length() + s2.length();

            // Store size of the new string
            // Technically sz + 1
            sz = s.length();
        }

        // If we need to move to start of the string
        else
        {

            // Take substring which will before
            // the inserted character
            String s2 = s.substring(0, ro);

            // Take substring which will be after
            // the inserted character
            String s3 = s.substring(ro, sz);

            // Insert into the string
            s = s2 + ch + s3;

            // Store new inserted position
            ind = s2.length();

            // Store size of the new string
            // Technically sz + 1
            sz = s.length();
        }
    }

    // Return the required character
    if (ind == 0)
    {
        return s.charAt(sz - 1);
    }
    else
    {
        return s.charAt(ind - 1);
    }
}

// Driver code
public static void main(String []args)
{
    char arr[] = { '1', '2', '3', '4', '5' };
    int k = 2;
    int n = arr.length;

    // Function call
    System.out.println(Insert(arr, n, k));
}
}

// This code is contributed by avanitrachhadiya2155

Python3

# Python3 implementation of the approach

# Function to insert the character
def insert(arr: list, n: int, k: int) -> chr:

    # To store last position where
    # the insertion is done
    ind = 0

    # To store size of the string
    sz = 0

    # To store the modified string
    s = ""

    # To store characters
    ch = arr[0]

    # Add first character to the string
    s += ch

    # Update the size
    sz = 1

    # Update the index of last insertion
    ind = 0

    # Insert all other characters to the string
    for i in range(1, n):

        # Take the character
        ch = arr[i]

        # Take substring upto ind
        s1 = s[0:ind + 1]

        # Take modulo value of k with
        # the size of the string
        temp = k % sz

        # Check if we need to move to
        # the start of the string
        ro = temp - min(temp, sz - ind - 1)

        # If we don't need to move to start of the string
        if ro == 0:

            # Take substring from upto temp
            s2 = s[ind + 1:ind + 1 + temp]

            # Take substring which will be after
            # the inserted character
            s3 = s[ind + temp + 1:sz]

            # Insert into the string
            s = s1 + s2 + ch + s3

            # Store new inserted position
            ind = len(s1) + len(s2)

            # Store size of the new string
            # Technically sz + 1
            sz = len(s)

        # If we need to move to start of the string
        else:

            # Take substring which will before
            # the inserted character
            s2 = s[:ro]

            # Take substring which will be after
            # the inserted character
            s3 = s[ro:sz]

            # Insert into the string
            s = s2 + ch + s3

            # Store new inserted position
            ind = len(s2)

            # Store size of the new string
            # Technically sz + 1
            sz = len(s)

    # Return the required character
    if ind == 0:
        return s[sz - 1]
    else:
        return s[ind - 1]

# Driver Code
if __name__ == "__main__":
    arr = ['1', '2', '3', '4', '5']
    k = 2
    n = len(arr)

    # Function call
    print(insert(arr, n, k))

# This code is contributed by
# sanjeev2552

C#

// C# implementation of the approach
using System;

class GFG{

// Function to insert the character
static char Insert(char[] arr, int n, int k)
{

    // To store last position where
    // the insertion is done
    int ind = 0;

    // To store size of the string
    int sz = 0;

    // To store the modified string
    String s = "";

    // To store characters
    char ch = arr[0];

    // Add first character to the string
    s += ch;

    // Update the size
    sz = 1;

    // Update the index of last insertion
    ind = 0;

    // Insert all other characters to the string
    for(int i = 1; i < n; i++)
    {

        // Take the character
        ch = arr[i];

        // Take substring upto ind
        string s1 = s.Substring(0, ind + 1);

        // Take modulo value of k with
        // the size of the string
        int temp = k % sz;

        // Check if we need to move to
        // the start of the string
        int ro = temp - Math.Min(temp, sz - ind - 1);

        // If we don't need to move to
        // start of the string
        if (ro == 0)
        {

            // Take substring from upto temp
            string s2 = s.Substring(ind + 1, temp);

            // Take substring which will be after
            // the inserted character
            string s3 = s.Substring(ind + temp + 1,
                               sz - ind - temp - 1);

            // Insert into the string
            s = s1 + s2 + ch + s3;

            // Store new inserted position
            ind = s1.Length + s2.Length;

            // Store size of the new string
            // Technically sz + 1
            sz = s.Length;
        }

        // If we need to move to start of the string
        else
        {

            // Take substring which will before
            // the inserted character
            string s2 = s.Substring(0, ro);

            // Take substring which will be after
            // the inserted character
            string s3 = s.Substring(ro, sz - ro);

            // Insert into the string
            s = s2 + ch + s3;

            // Store new inserted position
            ind = s2.Length;

            // Store size of the new string
            // Technically sz + 1
            sz = s.Length;
        }
    }

    // Return the required character
    if (ind == 0)
    {
        return s[sz - 1];
    }
    else
    {
        return s[ind - 1];
    }
}

// Driver code
static public void Main()
{
    char[] arr = { '1', '2', '3', '4', '5' };
    int k = 2;
    int n = arr.Length;

    // Function call
    Console.WriteLine(Insert(arr, n, k));
}
}

// This code is contributed by rag2127

Javascript

<script>
// Javascript implementation of the approach

// Function to insert the character
function Insert(arr,n,k)
{
    // To store last position where
    // the insertion is done
    let ind = 0;

    // To store size of the string
    let sz = 0;

    // To store the modified string
    let s = "";

    // To store characters
    let ch = arr[0];

    // Add first character to the string
    s += ch;

    // Update the size
    sz = 1;

    // Update the index of last insertion
    ind = 0;

    // Insert all other characters to the string
    for(let i = 1; i < n; i++)
    {

        // Take the character
        ch = arr[i];

        // Take substring upto ind
        let s1 = s.substring(0, ind + 1);

        // Take modulo value of k with
        // the size of the string
        let temp = k % sz;

        // Check if we need to move to
        // the start of the string
        let ro = temp - Math.min(temp, sz - ind - 1);

        // If we don't need to move to
        // start of the string
        if (ro == 0)
        {

            // Take substring from upto temp
            let s2 = s.substring(ind + 1,
                                    ind + 1 + temp);

            // Take substring which will be after
            // the inserted character
            let s3 = s.substring(ind + temp + 1, sz);

            // Insert into the string
            s = s1 + s2 + ch + s3;

            // Store new inserted position
            ind = s1.length + s2.length;

            // Store size of the new string
            // Technically sz + 1
            sz = s.length;
        }

        // If we need to move to start of the string
        else
        {

            // Take substring which will before
            // the inserted character
            let s2 = s.substring(0, ro);

            // Take substring which will be after
            // the inserted character
            let s3 = s.substring(ro, sz);

            // Insert into the string
            s = s2 + ch + s3;

            // Store new inserted position
            ind = s2.length;

            // Store size of the new string
            // Technically sz + 1
            sz = s.length;
        }
    }

    // Return the required character
    if (ind == 0)
    {
        return s[sz - 1];
    }
    else
    {
        return s[ind - 1];
    }
}

// Driver code
let arr=['1', '2', '3', '4', '5' ];
let  k = 2;
let n = arr.length;

document.write(Insert(arr, n, k));


// This code is contributed by ab2127
</script>

Output

1

Time Complexity: O(n²), where n is the length of the given string.
Auxiliary Space: O(n)