Encrypt a string by repeating i-th character i times

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Given string str, the task is to encrypt the string with the given encryption algorithm. The 1^st character of the string will be repeated once in the encrypted string, the 2^nd character will be repeated twice, …, n^th character will be repeated n times.

Examples:

Input: str = "zambiatek" 
Output: geeeeekkkksssss

Input: str = "abcd" 
Output: abbcccdddd

Approach: Initialize cnt = 1 and start traversing the string character by character. Repeat the current character cnt number of times then update cnt = cnt + 1 and get to the next character. Repeat these steps for every character of the string.

Below is the implementation of the above approach:

C++

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to return the encrypted string
string encryptString(string str, int n)
{
    int i = 0, cnt = 0;
    string encryptedStr = "";
 
    while (i < n) {
 
        // Number of times the current
        // character will be repeated
        cnt = i + 1;
 
        // Repeat the current character
        // in the encrypted string
        while (cnt--)
            encryptedStr += str[i];
        i++;
    }
 
    return encryptedStr;
}
 
// Driver code
int main()
{
    string str = "zambiatek";
    int n = str.length();
    cout << encryptString(str, n);
 
    return 0;
}

Java

// Java implementation of the approach
class GFG 
{
 
// Function to return the encrypted String
static String encryptString(String str, int n)
{
    int i = 0, cnt = 0;
    String encryptedStr = "";
 
    while (i < n) 
    {
 
        // Number of times the current
        // character will be repeated
        cnt = i + 1;
 
        // Repeat the current character
        // in the encrypted String
        while (cnt-- >0)
            encryptedStr += str.charAt(i);
        i++;
    }
 
    return encryptedStr;
}
 
// Driver code
public static void main(String[] args) 
{
    String str = "zambiatek";
    int n = str.length();
    System.out.println(encryptString(str, n));
}
}
 
// This code has been contributed by 29AjayKumar

Python3

# Python3 implementation of the approach 
 
# Function to return the encrypted string 
def encryptString(string, n): 
 
    i, cnt = 0, 0
    encryptedStr = "" 
 
    while i < n: 
 
        # Number of times the current 
        # character will be repeated 
        cnt = i + 1
 
        # Repeat the current character 
        # in the encrypted string 
        while cnt > 0: 
            encryptedStr += string[i]
            cnt -= 1
             
        i += 1
 
    return encryptedStr 
 
# Driver code 
if __name__ == "__main__":
 
    string = "zambiatek"
    n = len(string) 
    print(encryptString(string, n))
 
# This code is contributed 
# by Rituraj Jain

C#

// C# implementation of the approach
using System;
 
class GFG
{
     
// Function to return the encrypted String
static String encryptString(String str, int n)
{
    int i = 0, cnt = 0;
    String encryptedStr = "";
 
    while (i < n) 
    {
 
        // Number of times the current
        // character will be repeated
        cnt = i + 1;
 
        // Repeat the current character
        // in the encrypted String
        while (cnt-- >0)
            encryptedStr += str[i];
        i++;
    }
 
    return encryptedStr;
}
 
// Driver code
static public void Main ()
{
    String str = "zambiatek";
    int n = str.Length;
    Console.WriteLine(encryptString(str, n));
}
}
 
// This code is contributed by ajit

PHP

<?php
// PHP implementation of the approach 
 
// Function to return the encrypted string 
function encryptString($str, $n) 
{ 
    $i = 0 ;
    $cnt = 0; 
    $encryptedStr = ""; 
 
    while ($i < $n) 
    { 
 
        // Number of times the current 
        // character will be repeated 
        $cnt = $i + 1; 
 
        // Repeat the current character 
        // in the encrypted string 
        while ($cnt--) 
            $encryptedStr .= $str[$i]; 
        $i++; 
    } 
 
    return $encryptedStr; 
} 
 
// Driver code 
$str = "zambiatek"; 
$n = strlen($str);
 
echo encryptString($str, $n); 
 
// This code is contributed by Ryuga
?>

Javascript

<script>
    // Javascript implementation of the approach
     
    // Function to return the encrypted String
    function encryptString(str, n)
    {
        let i = 0, cnt = 0;
        let encryptedStr = "";
 
        while (i < n) 
        {
 
            // Number of times the current
            // character will be repeated
            cnt = i + 1;
 
            // Repeat the current character
            // in the encrypted String
            while (cnt-- >0)
                encryptedStr += str[i];
            i++;
        }
 
        return encryptedStr;
    }
     
    let str = "zambiatek";
    let n = str.length;
    document.write(encryptString(str, n));
         
</script>

Output:

geeeeekkkksssss

Time Complexity: O(n) // n is the length of the string

Auxiliary Space: O(1)

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